A TIA (transient ischemic attack) is a brief episode that causes the same type of symptoms as a stroke, but usually much less severe, not life threatening, and the symptoms are often temporary, or at least mostly reversible. The cause is not always identifiable, but is probably associated with a partial obstruction of a vessel that reduces the oxygen level in a part of the brain temporarily.
A CVA (cerebrovascular accident) or stroke, is caused by an event that causes more permanent damage to a larger area of the brain, resulting in more widespread damage and more permanent disability. Though many can recover to a great degree from a stroke, they can be fatal if they are widespread enough. The causes are usually a blockage of a major vessel that feeds the brain, or bleeding within the brain that causes pressure that damages surrounding tissue as well as deprives other areas of the blood that should have gone there.