Two events are dependent if the occurrence of one event has an effect on the probability the other event occurs.

When the occurence of one event does NOT have an effect on the probability the other event occurs, the events are said to be independent.

In a bag containing two red marbles and three blue marbles, if you draw a red marble without replacement (you keep the red marble out of the bag after it is drawn), the probability of getting a red marble on a subsequent draw is NOT the same as it was on the first draw.