Definition of flopper
When we say "flopper" we mean that our private cards (the 2 in Hold'em or the 4 in Omaha) have connected (or not) with the first 3 community cards, which we call the flop. If we have 56 in spades over AKJ in hearts, we say we didn't flop anything. If you still have 56 in spades and the flop comes 782, we say we flopped a straight draw. If the flop comes 4-2-A all in spades, we say we flopped a flush. Flopper refers to the relationship between our private cards and the community cards on the flop.
How often do you flop?
A good exercise is to calculate your probability of flopping this or that type of hand. For example, you have matching connectors; how often will you hit a straight draw? ?? how often will you hit a flush draw? ?? how often will you hit two pairs? ?? how often will you flop a three of a kind? You can use software like Flozilla to give you these results. With a hand like AK (or any hand that doesn't have a pair), you'll only hit a pair on the flop one out of three times, did you know that?