Used when to describe something you are referring to without actually letting the adjective you want to use be known. Means simply, a good thing or a bad thing. Used in many ways. It takes skill.
"Dude, did you see that chicks hair? NOT OPTIMAL." or
"OMG, did you see that hot guy just walk by? OPTIMAL."
1) someone just stepped in dog shit. NOT OPTIMAL
2) i just found the perfect dress. OPTIMAL