Two events are said to be independent if the occurrence of one event is in no way affected by the occurrence of the other event. Suppose we roll a die and receive a 6. The second time we roll the die, its outcome will not be affected by the fact that we received a 6 in the first roll. The outcome of each roll is independent of each other.
To be independent, one of the following conditions must be true:
P(A | B) = P(A) or P(B | A) = P(B)
If the two events are not independent, then they are said to be dependent, that is, the occurrence of one event influences the occurrence of another event.