777timesgod
Officially the unofficial Forum Censor
see also, "beater guitar"
Doesn't that term imply that the guitar is a cheap one, bought just for playing by a beginner or someone who wants to practise mods on it for the first time? It may have defects or have bad playability.
I would assume that a workhorse is a guitar you keep after you have bought more expensive pieces of gear because its dependability is appreciated.