Events are independent if knowing whether one has occurred does not change the
probability of the other.
Suppose you pick a card and toss a coin. The probability of getting a tail, P(T), in no
way influences the probability of getting a queen, P(Q), from a pack of cards.
$$P(T│Q)=P(T),\,and \,P(Q│T)=P(Q)$$
$$P(T∩Q)=P(T)×P(Q)$$