Smoky Mexican agave spirit, broader category than tequila.
Substitutes
Tequila — 1:1. Tequila is made from the same agave family. Lacks mezcal's smoky character.
Liquid Smoke — 1/4 tsp liquid smoke + 2 tbsp lime juice per 2 tbsp mezcal. For the smoky element in cooking, liquid smoke with lime juice approximates mezcal's character.
Bourbon — 1:1. Bourbon has different smoky notes (oak vs agave); add a drop of liquid smoke if desired.