Aloe barbadensis is another name for aloe vera, a medicinal plant of desert origin. It's widely used as a home remedy for burns and is also used as an ingredient in various skin care and beauty products. Aloe can be grown indoors as a houseplant; in some climates it also thrives outdoors, although it needs to be protected from both frost and excessive rain.
Botanically speaking, aloe is a leaf succulent. That is, it's a type of plant that has adapted to dry desert conditions by storing water in its leaves. In aloe's case, the water is stored in its gel-like sap. You can use the sap topically directly from the leaf -- simply slit it open and squeeze.
Aloe's sap is an effective skin moisturizer. It's also useful for treating burns, including sunburn. Aloe vera shows some anti-inflammatory properties that also make it suitable for treating certain skin conditions such as psoriasis and herpes outbreaks as well as minor skin irritations such as wind burn and razor burn. You can also use it as a preventative treatment before shaving or going outside in the wind or sun; don't use it as a substitute for sunscreen, however.
Although in the past aloe vera was used to treat constipation, the sap should not be taken internally. Keep it away from your mouth and your eyes when applying topically. Do not apply to open wounds.