Sub-5 confusion

[idontblamejordan]

Im relatively new to the community and am always confused when people use the term sub5.
also people saying sub5 is essentially the lowest rating doesnt make sense to me.
firstly sub5 on which scale? on both it wouldnt be below ltn as a rating.
thanks for answering

 

[s7seveenn]

sub 5 = ltn
AKA 97th -50th percentile of humans
AKA Below Average but not absolutely hideous