Tequila is Mezcal but Mezcal is not Tequila.
Mezcal ad Tequila are both agave-based liquors. However, Tequila can only be made from one type of agave. Unlike Tequila, Mezcal is a spirit that can be produced fro mupwards of 28 varieties of the agave plant. The flavor profile is very different than Tequila because it is typically smokier. If you are a Scotch drinker, Mezcal is to Tequila what Scotch is to Whiskey.