A back bevel keeps the section of the blade behind the edge thinner, which improves cutting quality. You can get a knife with a single bevel or a double bevel.
A knife bevel refers to a surface that has been ground to form the knife’s edge. A close inspection of a knife will show a slight angle on either side that runs down to the edge. This is the bevel. If there is one on both sides, then it is a double bevel knife. If there is one on only one side, then it is a single bevel knife. You can grind the bevel to a variety of different angles. Generally, the smaller the angle, the sharper the knife.