Backbone -
The top level in a hierarchical network. Stub and transit networks that connect to the same backbone are guaranteed to be interconnected.

Browser -
A program that lets you display a file containing hypertext and graphic images. The browser also lets you navigate from one hypertext file to another via links using URLs.

Cache -
Memory holding recently accessed data, designed to speed up subsequent access to the same data. The term cache is often applied to processor-memory access but can also be used to indicate a local copy of data Internet accessible within a network.

Client -
A computer system or process that requests a service of another computer system or process (referred to as a server). For example, a workstation requesting the contents of a file from a file server is a clientof the file server.

Cookie -
A handle, transaction ID or other token of agreement between cooperating programs.

An HTTP cookie is data sent by an HTTP server to a browser and then sent back by the browser each time it accesses that server. Cookies can contain any arbitrary information the server chooses and are used to maintain a state (i.e., a computer's configuration, attributes, condition or information content) between stateless HTTP transactions.

Typically an HTTP cookie is used to authenticate or identify a registered user of a web site without requiring an additional sign-in every time that site is accessed. Cookies are also used to maintain a "shopping basket" of goods selected for purchase during a session at a site, to personalize a site (i.e., presenting different pages to different users), and to track a particular user's access to a site.

Datagram -
A packet format with Internet headers defined by the Internet Protocol (IP). Datagrams are self-contained, independent entities carrying sufficient information to be routed from the source to the destination computer without relying on earlier exchanges between this source and destination computer and the transporting network. Datagrams are small and of a fixed size.

Data Packet -
The basic unit of information exchange between computers engaged in data communications.

De Facto Standard -
A widespread consensus on a particular product or protocol that has not been ratified by any official standards body, such as the International Organization for Standardization (ISO), but which nevertheless has a large market share. The ISO is a voluntary, nontreaty organization founded in 1946 that is responsible for creating international standards in many areas, including computers and communications.

Domain -
Refers to a group of computers whose hostnames share a common suffix, the domain name. Some important domains are .com (commercial), .edu (educational, mostly U.S.), .net (network operations), .gov (U.S. government) and .mil (U.S. military). Most countries also have a domain, for example, .us (United States), .uk (United Kingdom) and .au (Australia).

Domain Name System (DNS)-
A general-purpose distributed, replicated, data query service chiefly used on the Internet for translating hostnames into Internet addresses. Also, the style of hostname used on the Internet (though such a name is properly called a fully qualified domain name). DNS can be configured to use a sequence of name servers, based on the domains in the name being looked for, until a match is found.

The Domain Name System refers to both the way of naming hosts and the servers and clients that administer that information across the Internet.

Dynamically Assigned Host Address (DAHA) -
An Internet Service Provider proprietary method of assigning IP addresses when a member signs on. An IP tunnel server assigns the address and allows the member access to the Internet.

Handle -
A number or token that lets a program access a resource. Programs often receive a handle in response to a request for a resouce, and then they use the handle when they need to access the resource. When the program uses the handle, the value of the handle tells the system which resource, from the pool of resources maintained by the system, to use.

Hostname -
The unique name by which a computer is known on a network. The hostname is used to identify the computer in electronic mail, Usenet news, or other forms of electronic information exchange.

On the Internet, the hostname is an ASCII string, e.g., AWD.myhost.up24-7.net, that consists of a local part (AWD.myhost) and a domain name (up24-7.net). The hostname is translated into an Internet address via an application like Domain Name System (DNS). It is possible for one computer to have several hostnames (aliases) though one is designated as its standard or primary name.

Hypermedia -
An extension of hypertext that includes graphics, sound, video and other kinds of data.

Hypertext -
A collection of documents (or nodes) containing cross-references or links which, with the aid of an interactive browser program, let the reader move easily from one document to another. See also hypermedia.

HyperText Markup Language (HTML) -
The markup language with which World Wide Web (WWW) documents are written. HTML lets you create hypertext links, fill-in forms and clickable images (i.e., images that you click to access another area).

HyperText Transfer Protocol (HTTP) -
An application-level protocol for distributed, hypermedia information systems. HTTP/1.0 is the version presently used. HTTP/1.1 is in pre-release stage.

Internet protocol (IP) -
A protocol that enables packets of data to be transmitted throughout the Internet using the transmission control protocol (TCP). A data entity is broken into individual packets. Each packet is wrapped with header information that indicates where the packet came from, where it is going, and what part of a whole entity it belongs to. Once the packets arrive at their destination, they are reassembled into their original order by TCP.

IP address -
Internet protocol (IP) address. A unique 32-bit number specified as four 8-bit numbers (represented as integers) called octets. The four octets are connected by periods. The numbers must be in the range 0-255. A sample IP address is 255.32.3.10.This address is often assigned by a government agency called the DDN Network Information Center (NIC).

Lossy -
Refers to a data compression algorithm that actually reduces the amount of information in the data, rather than just the number of bits used to represent that information. The lost information is usually removed because it is subjectively less important to the quality of the data (usually an image or sound) or because it can be recovered reasonably by interpolation from the remaining data.

Origin server -
A server on which a given resource resides or was created.

Protocol -
A set of formal rules describing how to transmit data, especially across a network. Low-level protocols define the electrical and physical standards to be observed, bit- and byte-ordering and the transmission and error detection and correction of the bit stream. High-level protocols deal with the data formatting, including the syntax of messages, the terminal-to-computer dialog, character sets, and sequencing of messages.

Proxy -
An intermediary program that acts as both a server and a client for the purpose of making requests on behalf of other clients. Proxies are often used as client-side portals (i.e., a trusted agent that can access the Internet on the client's behalf) through the network firewall and as helper applications for handling requests via protocols not implemented by the user agent.

Server -
An application program that accepts connections in order to service requests by sending back responses.

Sub Network -
A network that only carries packets to and from local hosts. Even if it has paths to more than one other network, it does not carry traffic for other networks.

Transit Network -
A network that passes traffic between other networks in addition to carrying traffic for its own hosts. It must have paths to at least two other networks.

Transmission Control Protocol/Internet Protocol (TCP/IP) -
The de facto standard Ethernet protocols incorporated into 4.2BSD UNIX and developed by the Department of Defense (DOD) for communications between computers. The DOD's Defense Advanced Research Project Agency (DARPA) developed TCP/IP for internetworking, encompassing both network-layer and transport-layer protocols. While TCP and IP specify two protocols at specific layers, TCP/IP is often used to refer to the entire DOD protocol suite.

Uniform Resource Locator (URL) -
A text string of a standard format that describes the address of a networked resource. There are two basic types of URL formats that are prefixed: http://www(Internet type).

User Agent -
The client that initiates a request. User agents are often browsers, editors, spiders (web-traversing applications) or other end-user tools.

Web Site -
Any computer on the Internet running a World Wide Web server process. A particular web site is identified by the hostname part of an URL. Multiple hostnames may actually map to the same computer, in which case they are known as virtual servers.

Wrapper -
An envelope placed around a data packet, which typically provides new header information including destination and source address information. Wrappers are often used to transport one type of packet through a different network protocol.