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.

When I had problems with my fingers, and more recently, with my back, I took therapy that consisted of exercises and even heat. Generically, this is referred to as physical and occupational therapy.

In this sense, the exercises were not meant to occupy persons who have nothing else to do, but to help people whose occupations lead to physical problems--today many will suffer repetitive stress injuries and carpal tunnel syndrome.

Maybe, some people don't care about what they are doing--certainly many information technologists have nothing invested in their work; others have a greater involvement in what they do, and seek not to experience pain when they do it, and even more, to be efficient when they do it--playing the piano, for instance.

Occupational therapy is using occupation (meaning the performing of activities with specific goals), to help people prevent, lessen, or overcome physical, neurological and psychosocial disabilities.