Data transfer
In Web hosting, the total size of files transferred by an account in a month.

Database
Data in a structured format stored on a web server.  When we speak of databases for web hosting we are usually talking about web sites that need to add, delete, and update large quantities of information via the web. There are many different types of database systems available. Some of these include MS Access, MySQL, SQL Server, and Oracle Databases. If you plan on using ASP more than likely you will need your hosting company to have a database.

Dedicated Server
Similar to co-location, except that you lease or rent hardware from a Web host.  A dedicated server is one that a web hosting company has dedicated to a single client. In other words, only one client can access that server and that company’s site is the only one residing on that server.

DHCP
Dynamic Host Configuration Protocol. An automated way of obtaining an IP address in the Local Area Network.

Dial up
Dialup access is a way of connecting a computer to the Internet using a modem and the telephone line. It is rather slow and blocks the telephone line.

DNS
DNS stands for Domain Name System and is a distributed, replicated system which allows nameservers to map domain names to an IP number.

Domain name
Domain name is an easy-to-remember address that can be translated by DNS into server's IP address.  The unique name that identifies an Internet site. Domain Names always have 2 or more parts, separated by dots. The part on the left is the most specific, and the part on the right is the most general.

DSL
Digital Subscriber Line. A better way of connecting a computer to the Internet using the telephone line. It's faster than the dialup and doesn't block the telephone line. However, it is more expensive because the special equipment is required.