What is the difference between a cactus and a succulent?

Cacti are fleshy plants that keep water, making them part of this group. All cacti are succulents. In order for a succulent plant to be considered  a cactus, the plant needs to have areoles. Areoles are small, rounded, cushion-like mounds of flesh where spines, hair, leaves, blossoms, as well as a lot more grow from the cactus.