A program or device—browsers, robots, hardware, software—used to access the Internet. By extension, a “reasonable” user agent provides support for core W3C standards , whereas a “somewhat reasonable” user agent supports HTML 32. Moreover, Web browsers not providing support for HTML 3.2 are considered to be, at best, “broken” software. The term user agent is also used to describe a mail program such as Outlook or Eudora that sends and receives e-mail on a user’s behalf.
Bartlett, K. User Agent. [Online, April 11, 2006.] HTML Writer’s Guild Website. http://www.hwg.org/opcenter/events/oldevents/fedweb/04.html.