Whenever we give plant advice on how to keep a plant happy, the standard we give it so provide your plant with an environment as close to its natural habitat as possible. Most cacti live in habitats that do not get much water. Many live in extremely dry environments, in cold and warm climates, at sea level and on mountain tops throughout the Americas. It is estimated there are over 1700 different species that make up the Cactaceae family.
Given their special adaptation to store water for a not-so-rainy day, cacti, are indeed, a type of succulent. However, not all succulents are cacti. The distinguishing factor between cacti and other succulents is that cacti only store water in the fleshy parts of their trunk or stem. Other succulents have leaves in which they store water in addition to their trunk or stem. Cacti do not; their leaves are actually highly modified into spines that grow from areoles on the surface of the plant. Photosynthesis (making food from sunlight) does not typically occur in the spines of cacti, like it would in the leaves of most plants, rather it occurs in the stem or trunk of the cactus.