Prerelease software version (4)
I believe the answer is:
beta
'prerelease software version' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for beta that I've seen before include "testing stage" , "Second Greek letter - beat that" , "Second-rate" , "Greek letter -- second in order of importance" , "2nd letter of Greek alphabet" .)