What does it mean to call a line "sharp"? I am a chess newbie and I was watching a video on four knights opening and the person was discussing another variation and he said that one is dramatic and quite sharp.  From what I saw, it seems "sharp" means immediate mating threats. 

Wiki has this: 

"Risky, double-edged, highly tactical. Sharp can be used to describe moves, maneuvers, positions, and styles of play."

https://en.wikipedia.org/wiki/Glossary_of_chess#S

That definition, if correct, is still sort of vague for me.  Does it mean Kasparov plays sharp because he was very good at tactics?  Or if you go for Scholar's Mate, does that mean you're using a sharp line?  Can someone elaborate on the meaning of sharp more, like what makes a line sharp, maybe with examples?  Thanks.
A sharp position is one where every move is critical and any mistake could be your last; in such positions basic principles take a back seat to calculation. The opposite of a sharp position is a calm position, where you have time to maneuver as you please and arrange your pieces as you want before initiating confrontation.