ID may refer to any of the following:

  1. In general, an ID is an abbreviation for identification. Identification is the act of being identified so a system can verify whom you say you are. For example, many services require a valid username and password before the system can be accessed. If the correct username and password are entered, you are identified and can log in.

  2. With BSD, id is a command to show the numeric user and group ID on BSD. See our id command page for further information and examples on this command.

  3. With CSS, id is a selector used to specify a style on one HTML element. For example, the id below called “center” could be created to center text on a paragraph of text. However, once an id is used on an element, it cannot be used with any other element. If you need to use a style on more than one element, use the class selector.

CSS id code

#center { text-align: center; }

HTML

tag with center class

This text would be centered.

As shown in this CSS code, every CSS id is prefixed with a pound symbol in front of the id name. A line that does not begin with a pound is considered an HTML tag selector and a class selector begins with a period.

  1. When referring to a company, id is an abbreviation for id Software.

Never start a CSS id with a number since not all browsers support id names beginning with numbers.

  1. The Internet domain suffix .id is short for Indonesia.

Attribute, Computer abbreviations, Operating system terms