Deathtouch
Keyword abilities
Any amount of damage from this source is lethal.
How it works
A creature dealt any nonzero amount of damage by a source with deathtouch is destroyed the next time state-based actions are checked, regardless of its toughness.
Deathtouch cares about the source of the damage, so it applies to combat and noncombat damage alike (a deathtouch creature that pings, or a Pithing-style ability granting deathtouch).
Common confusions
“Does 0 damage from a deathtouch source destroy a creature?”
No. Deathtouch needs at least 1 damage dealt. Effects that reduce damage to 0, or assigning 0, won't trigger it.
“Deathtouch vs. indestructible.”
Indestructible wins. The creature is dealt 'lethal' damage but can't be destroyed, so it survives.
“Deathtouch with trample.”
Only 1 damage per blocker counts as lethal, so a deathtouch-trampler can push almost all of its damage past blockers.