I've not heard the term applied to a skirt, but it is a known label for a type of short jacket worn by men in the 1960s, and re-popularised by David Bowie during his 'white soul' period. If you check out the cover of the 'David Live' album, that's a 'bumfreezer' jacket he's wearing.
It's an Eton jacket. Also used for the short ventless Italian-style jacket worn by stylish proto-Mod types in the late 50s. Read Colin McInnes's Absolute Beginners for details.