Definition of good run
A "good run" or "run good" is a short or long pass during which one is lucky. When we are in a good run, we have the aces and our opponents have the kings, we have stronger brelans than our opponents, we have colors to the ace when our opponents have colors to the king, in short, we have the momentum, the wind in the sails. The "good run" is opposed to the "bad run", a pass during which our aces are cracked and during which no matter how strong our hand is, we always have the second best hand.
The good run and the bad run, it's all in our head.
Obviously, the cards have no memory. If you have 3x the aces in 3 hands, it's good run, but in reality, it's only your mind that notices it because you'll have all 221 aces in the long run. The good run and the bad run exist only in our head so you shouldn't give it too much importance. On the other hand, it can give you a certain momentum. If you win 4 big pots in 15 minutes, it may discourage some players from playing against you.