There are 2 main classifications of Tequila - Mixto and 100% Puro de Agave. Both of these can be further classified into one of 4 other styles; Blanco, Reposado, Anejo or Extra Anejo.
Mixto - mixed Tequila made from a minimum of 51% agave. The other 49% can be any other source of fermentable sugars (often molasses) and must be added before the fermentation stage. This Tequila is also known as Gold in the U.S. and Joven Abocado in Mexico. We would not recommend ever buying or drinking this style of Tequila.
100% Puro de Agave - 100% Pure Agave Tequila made entirely from Weber Variety Blue Agave. If it doesn't say 100% Puro de Agave on the bottle then it's not made from 100% Agave.
Blanco, Silver, Plata, Platinum - white or silver Tequila that is usually not aged at all but can be aged for less than 2 months in barrels of any size.
Reposado - rested Tequila that has been aged for at least 2 months and no more than 12 months in wooden barrels of any size.
Anejo - aged Tequila that has been aged for at least 12 months in oak barrels no larger than 600 liters.
Extra Anejo - extra aged Tequila aged for a minimum of 3 years in oak barrels no larger than 600 liters in size.