Cannabis oils are extracts from cannabis plants. Unprocessed, they contain the same 100 or so active ingredients as the plants. but the balance of compounds depends on the specific plants the oil comes from. The two main active substances in cannabis plants are cannabidiol. Or CBD, and delta-9 tetrahydrocannabinol, or THC. Oil extracted from hemp plants can contain a lot of CBD. While oil from skunk plants will contain far more THC. THC produces the high that recreational cannabis users seek. While oils for medical use contain mostly CBD.
How is it different from cannabis?
Other forms of cannabis are solid and are usually sold either as resin or dried plant material. In commercially-produced medical cannabis oils, the concentrations of CBD and THC tend to be well-controlled, which makes it easy to calculate doses.