The word copal is derived from the Nahuatl language word copalli, meaning incense. Copal incense is burned on Día de Muertos to guide the dead back to their homes. The incense is somewhat smoky when burned and has sort of a pine scent. The copal was offered by the indigenous peoples of the Oaxaca region to their gods and is used to cleanse the place of evil spirits and thus the soul can enter your house without any danger.
Copal incense is sold in bulk in community markets in the Oaxaca region. A number of hardened tree resins are used as aromatic incense, these resins are considered the "blood of trees".
Copal incense is typically burned over charcoals in a tripod brazier. In the Zapotec world, smoke is what translates material things from our world into the spirit world.