lq-text is a full-text retrieval package. The project makes an inverted index of your files, and can then later find words or phrases in those files. This is also sometimes called a full-text (or fulltext) database, or an information retrieval system. I don't use those terms because lq-text is not ACID-compliant (database), and the phrase "information retrieval" seems overly broad.
lq-text can produce extracts from the files it matches, for example highlighting every occurrence of matched words, or producing one-line keyword-in-context (KWIC) indexes.
A higher level summary might say that lq-text is a search engine used in text information retrieval systems, based on a fulltext index.
lqaddfile -- add files to the database at any time
lqfile -- information about files that have been indexed
lqword -- information about words
lqphrase -- look up phrases
lqrank -- combine phrase searches, and sort the results
lqquery -- supports wildcards in phrases, after running "sortwids"
sortwids -- run after lqaddfile to enable lqquery
lqkwic -- creates keyword-in-context indexes (this is fun!)
lqshow -- show the matches on the screen (uses curses)
lqwordlist -- search the stored vocabulary
lqtext -- curses-based front end.
lq -- shell-script front end
lqcat -- fetch and print files by lq-text FID or document name