Decision coverage

With Decision coverage the possible outcomes of of the decision are tested at least once. This means that  the result of the decision is one time true and false. In other words we cover one time the THEN and one time the ELSE.
 
It is relevant to vary in the outcome of the decision, not necessarily in that of the conditions. Since there are only two possible outcomes of a decision (THEN or ELSE), decision coverage results in 2 test situations per decision point.

 
See the following animation for a more detailed explanation: