The text adventure genre started by Crowther and Woods' Colossal Cave adventure in 1972. "Text Adventures" is often used interchangeably with "Interactive Fiction".
Playing text adventures involves typing plain English and reading textual responses, although it is not uncommon to find graphics inserted with the text, or commands given by the mouse.
The genre has blossomed to include a huge variety of games: difficult puzzles or no puzzles; inspired, evocative, funny, or terse writing; and also a few arcade games. More games are available every week, and there is an Interaction Fiction Competition every year.
This category includes illustrated text adventures with a command line interface.
Paul O'Brian's Interactive Fiction page, featuring the games and reviews he's written, information about the webzine he edits, and lots of nifty IF stuff. http://ucsu.colorado.edu/%7eobrian/IF.htm
Lots of classic 1980s computer software for sale/trade, specializing in Infocom text adventures. Monthly collector's column, waiting list, links to other software collectors' pages. http://www.if-legends.org/~yois/
The page for classic text adventure afficionados. Covers Scott Adams, Brian Howarth, Infocom, Level 9, and Magnetic Scrolls. http://www.if-legends.org/~pdd/
Ranked and annotated items, covering academic articles, fan or community web sites, influential amateur articles, and references to text adventures in mainstream literature. Focuses on the cultural and literary significance of text adventures. http://www.uwec.edu/jerzdg/orr/articles/IF/bibliography/index.html
Annual competition for games which exclude traditional "game elements" from entries, and also try to lift any plot as much as possible. http://members.aol.com/iffyart/