Updated: 04/26/2017 by Computer Hope

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, if a service or system is protected with a username and password and the correct username and password are entered, you are identified and can log in to the service or system.

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 <p> tag with center class

<p id="center">This text would be centered.</p>

As can be seen in the CSS code above, every CSS id needs a pound symbol in front of the name of the id to be defined as an id. A line that does not begin with a pound is considered an HTML tag selector and a class selector begins with a period.


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

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