P(A|B) denotes the conditional probability. In simple words, P(A|B) represents the probability of event A, considering that event B has already occurred. Conditional probability also shows that the probability of event A is influenced by occurrence of event B, which makes event A and B dependent events.
If the conditional probability of A given B is equal to probability of event A, as given in question, this shows that event A is not affected by event B or the two event are not dependent because the probability of event A is same both in presence of event B and in absence of event B.