Limfac is a short form for "limiting factor," often used by technicial and military people to describe a device or procedure's weakest or least efficient part. See also achilles heel.
The car's tiny engine was the limfac for it's ability to accelerate.
A spoken word derived from the abbreviation for Laughing My Fucking Ass Off (L.M.F.A.O). It can be used in context with the spoken word Roffle. Most often a response when someone says something funny or when "Roffle" is said.
Man: Oh man, that was so funny!
Woman: ROFFLE!
Man: LIMFAO!
Girl: Roffle limfao!