Randomness, or (if there is an element of repetition to it) spamming, or (if it appears random but is actually predicted) psychicness, is a property of playing certain moves; it is done without confirming that the opponent is potentially open (or without hit confirming).
This especially refers to special moves and super special moves that are risky; less consequential randomness is flailing (which does not have a negative stigma to it like randomness does).
Moves that can be used too safely just by spamming them (e.g., if they have an invincible hitbox and don’t leave the user open) are a definite balance breaker.
Two sorts of situations come up where otherwise straight-laced players may resort to randomness:
These tactics should not be used often, because they work best when the opponent does not expect them at all. Moreover, the former case is not exactly smiled upon by many.