The traditional Mexican stone tool used to mash avocados for guacamole is a molcajete.
A molcajete is a stone mortar traditionally paired with a hand-held pestle called a tejolote. It is commonly carved from vesicular basalt, a porous volcanic rock, and is used to crush chiles, herbs, spices, tomatoes, and avocados. Its rough surface helps grind ingredients into a textured paste rather than the completely smooth purée produced by many blenders.
Molcajetes have deep roots in pre-Hispanic Mesoamerica, where related stone grinding tools were used by cultures including the Aztec and Maya. Modern examples are often round and supported by three short legs, and some are decorated with animal heads. The matching tejolote is the tool that actually presses and grinds the ingredients inside the bowl.
A metate is another Mesoamerican grinding tool, but it is a large, usually flat stone slab used with a mano, traditionally for processing maize and other foods. A comal is a flat griddle, while a tostador is a roaster. None is the specific mortar-and-pestle tool associated with traditionally preparing salsa and guacamole.