A recruitment (or "recruit") is a thread posted in TG to attract interested players to a potential PbP game. Anyone interested in the core concept of the game (which is usually explained in the thread's original post, or OP) submit characters. The GM will review the submitted character sheets, provide advice and constructive criticism, and eventually select a party for the game thread. Selection is also known as "making picks".
GMs must be wary when posting recruits, because there are always people who do not bother reading the OP and fail to understand the game's setting, the character creation rules, and the intended tone of the game. Worse still are those who refuse to admit they are wrong when they make those mistakes, and almost try and harass the GM into changing the game purely to suit the player's own idiocy.