Detonate is a one-shot effect from an old red sorcery (the card Detonate itself), not a true keyword ability. It lets you pay X plus the mana cost and destroy an artifact with converted mana cost (mana value) equal to X. That artifact can't be regenerated, and Detonate also deals damage to the artifact's controller equal to its mana value.
The nuance people miss: you choose X when casting, and X must exactly match the target artifact's mana value—you can't destroy a higher-cost artifact by overpaying, nor a cheaper one by underpaying. The damage is a bonus tied to that same value, so it scales with how expensive the target was.
In Commander, it's niche artifact removal that doubles as a small damage source—handy against mana rocks or pricey artifact bombs, but rarely a maindeck staple given better modern options.