Fuse #47 in my 1997 Civic
 

The car's diagram says radio and back up on it.
Online it says "Audio unit, clock, TCM (CVT), ECM/ PCM (VBU)"

Obviously audio unit is the radio and clock is for the clock (neither exist anymore in the car)

But what does it mean "back up" and what are all the abbreviations?

The reason I ask is, the fuse was blown and I want to know what wasn't working before I replace the fuse so I know what im fixing