Definition of rush
We'll call it a rush when, over several hands, you have very good hands. Imagine that in 10 hands you have 2 AA preflop, 1 KK preflop, hit a 7-7-8 flop with 78 in hand and hit a 9-A-9 flop with A9 in hand. You'll probably win all the pots and we'll say you're on a rush. A rush is doubly profitable. Why double up? One, you have great hands so you'll be favored to win the pots. Two, because if your opponents see you playing almost every hand in succession, after a few hands they'll think you're exaggerating or tilted. So they'll start calling you light.
The card rush when no one sees your cards
Sometimes you will be in a card rush and no one will see your cards. For example, you go for a 4 bet preflop and your opponent folds. Then you flop a bet in another pot and your opponent folds again. If this is the case, since no one has seen your cards, players may start to suspect you of bluffing. If you are still in a rush the next few hands, don't hesitate to overbet with your very strong hands; your folding equity will be greatly reduced.