Software test stage (4)
I believe the answer is:
beta
'software test stage' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for beta that I've seen before include "Character between alpha and gamma" , "character in Marathon" , "Old character" , "Greek character - not quite top-notch" , "In a constellation, a star second in brightness" .)