IFDB, the Interactive Fiction Database, is a web site created by Mike Roberts in October 2007 for person-to-person recommendations about IF games. IFDB users can edit the database of games, create Recommended Lists, associate "tags" (keywords) with the games, add reviews and ratings, etc. There's also a tool called the Download Adviser, which makes it easier to download and install games. See the R*IF thread.
In September 2009, a major upgrade added several new features to IFDB. Users can now add competition pages, award pages, club pages, and news items. There's also more places to add comments, see who's playing what (subject to privacy settings), several RSS feed options, displays of tag counts, and a new option to mark games you're not interested in.
A TUID is a tads.org unique identifier, used by IFDB to uniquely identify a game in its database. It may be up to 16 characters long, a random mix of letters and digits assigned by the IFDB software when the game's page is created. The TUID for a game is listed in the Details section of a game page on IFDB. See What's a TUID? for more info.