Demonstration of a burned Wyld card creating an "exploded" dice roll (click for animation)
When rolling dice in combat, the term explode' is used to describe an outcome that, in addition to whatever it normally does, automatically grants a bonus die that is then immediately rolled. Wyld symbols explode (and count as an attack) as long as you aren't Corrupted (if you are, Rot symbols do instead), whereas Moon Scythe or Aflame will allow other symbols to explode under the proper conditions.
Explode Pool[]
When a dice explodes, it expends one of your Explode Pool for the combat/peril - once this is depleted, dice will no longer explode. (Your Explode Pool refills after every combat/peril). Normally, a creature's Explode pool is equal to their Spirit stat. Some Equipment can modify your Explode pool, as can the Trickery Cards Devious Ruse and Saboteur. In addition, Corrupted creatures, including Banes and the King of Armello, have an Explode pool equal to their Rot instead.