Difference between Slav and Semi-Slav

Hello. I've been thinking about what chess openings to play and my chess teacher recommended the Slav or Semi-slav. What's the difference between them? Which one would you recommend? I'm about 1800 by the way. Thanks.

Semi slav is much sharper so that would be the fighting choice while the slav proper gets the bishops out to f5 and usually b4 and should equalize, but black doesn't get as many chances to win. It looks like the diagram on the bottom.

Watch the e7 pawn in the opening. If that e7 pawn goes to e6 in the first few moves its the semi slav else if its just the c7-c6 pawn it could be the slav.

semislavs occur 10s more often than slavs in opening play. At least at my level.

I think it's fairly practical to let white decide.  You can play the slav and cut down a lot of theory by only playing the semi-slav against an early e3 by white, so you dont have to learn any of the super-sharp stuff where the white bishop goes outside the pawn chain.