A term coined by SimonTatham, e.g. at http://www.chiark.greenend.org.uk/~sgtatham/timber.html , to describe software written and used almost entirely by one person.
It evolves to provide exactly that set of features required by the author, often because a task is repeated several times and appears to be worth automating.
Keyboard maps or command line options will be obscure of course. There will be bugs which, if you trigger them you will be told "oh that isn't supported, don't do that".
Documentation, if any, will be hastily written for the benefit of those who download the program after the point when the author decides that others may benefit from it enough to offer it for download.
Horrible explanation, sorry. I've been meaning to BrainDump? that one for a while because it's such a lovely term. My apologies to Simon if I've misrepresented his meaning. 8-) -- MatthewAstley
See also DogFood.