There are two definitions of occupational therapy:

1. The original meaning of the word is the type of therapy organized for prisoners and people with a psychological disorder. The aim of the therapy is to keep the people busy with some sort of activity like making the pegs manually, knitting or pottery and making figures out of clay.
2. Nowadays it is used in a broader sense and with some degree of sarcasm: occupational therapy is applicable to anybody who's doing something that doesn't really make sense, isn't particularly useful, or some activity you like performing but nobody cares about at all...(does this sound familiar?)
Example: I've set up a webserver on one of the machines in the testlab. The site is only accessible via our intranet, and the information on the pages is only useful to my colleges who are sitting right beside me... but it gave me something to do to kill my more than sufficient amount of slacktime at work.