Economic term definition please?

Marginal benefit is the benefit you get from the last one of the goods you consumed (or bought, etc). Marginal benefit is generally umed to be decreasing, so the more you get, the less each new one pleases you. It is possible that this continues to the point where the last one consumed actually causes disutility (discomfort or pain), so the marginal benefit is negative. Consider food, it is possible to eat so much that more will cause you pain. Net positive marginal benefit means that the benefit obtained from the last good is not negative and is greater than zero (so some benefit is obtained).