What mean "Sharp"?
The meeting is at 7 o'clock sharp.

I think meanig in here "Exactly"
The meeting is at exactly 7 o'clock.

Question

What mean "Sharp"?
The meeting is at 7 o'clock sharp.

I think meanig in here "Exactly"
The meeting is at exactly 7 o'clock.

Answer

You are correct. Another expression that's used is "on the dot." 7 o'clock sharp and 7 o'clock on the dot mean the same thing.

Answer

Shayne already answered perfectly, I just would like to add: Sharp, in other contexts may mean that has an edge very prone to cutting, such as a knife or an axe

Eg.: This axe is very sharp

And it can be used as a way of saying "clever".

eg.: Mark is quite sharp on his answers