What is the difference between theoretical and experimental probability?

Theoretical probability is what you would expect the result of an experiment would be. For example if you tossed a fair coin 10 times the theoretical result would be 5 heads and 5 tails, because probabilty of 1 toss is 1/2 for tailand 11/2 for a head.

I practice however we might get, say, 6 heads and 4 tails

So experimental probability of e head would be 6/10 and of a tail would be 4/10.