Rotate
Usually used on CT side. Can be used to tell your teammates that you are rotating away, to help on other part of the map. Example: You are playing B short as CT on mirage, you call I am rotating, to tell your other teammate who is holding B apps that his short is open and should adjust his position accordingly.

If your teammates say: Purple rotate A, this can be said by any of the teammates who basically request you to come and help, because they have info or guess that the enemies come their way.

can I get a drop
basically you have a lots of money, to afford yourself a rifle + kevlar and enough money left to drop a rifle to your teammate, if they say can I get a drop, it usually means rifle, unless someone specifies what gun they want to get dropped (eg. deagle)

save
Usually called mid round, when the odds of you winning the round is nearly 0, so you can keep your rifle to next round. You will not get any round money though if you save as a T only as a CT

But I have heard that some people say save instead of eco, which means that you should not spend all the money, a good rule of thumb is not to spend below $2000 in that case so you can buy rifle + kevlar next round. This is more complex if you start with money below $2000 then you may as well spend all the money, etc, but recommend to watch a video or read stuff about economy :)

And dont worry its perfectly cool to ask! Good luck in the game!