Definition from Wiktionary, the free dictionary
bikeshed (plural bikesheds)
- (literally) An enclosed structure where bicycles may be stored.
- (figuratively, technical jargon) A metaphor for arguing endlessly over details of some small and relatively unimportant thing, taking up time that could be better spent on other things. The gist is that while nobody will question the details of a large and complex project (e.g. a nuclear reactor), for a simple thing as a bikeshed everybody will loudly add their two cents as to exactly how it should be built/painted/constructed, ad nauseum.
Originates from the 1960s, via the book Parkinson's Law, by C. Northcote Parkinson; popularized via the FreeBSD mailing lists.