Trample

Trample is a Keyword Ability that changes the rules for the Combat Damage Step, which allows the creature that has it to damage the opposing player even if it is blocked. When combat damage is resolved, if the power of the creature with Trample is greater than the combined toughness of the creatures blocking it, the defending player takes damage equal to the difference.

From the Comprehensive Rules:

• 502.9. Trample
  • 502.9a Trample is a static ability that modifies the rules for assigning an attacking creature’s combat damage. A creature with trample has no special abilities when blocking or dealing noncombat damage. (See rule 310, “Combat Damage Step.”)
  • 502.9b The controller of an attacking creature with trample first assigns damage to the creature(s) blocking it. If all those blocking creatures are assigned lethal damage, any remaining damage is assigned as its controller chooses among those blocking creatures and the defending player. When checking for assigned lethal damage, take into account damage already on the creature and damage from other creatures that will be assigned at the same time (see rule 502.9e). The controller need not assign lethal damage to all those blocking creatures but in that case can’t assign any damage to the defending player.
  • 502.9c If all the creatures blocking an attacking creature with trample are removed from combat before the combat damage step, all its damage is assigned to the defending player.
  • 502.9d Assigning damage from a creature with trample considers only the actual toughness of a blocking creature, not any abilities or effects that might change the final amount of damage dealt.
    Example: A 6/6 green creature with trample is blocked by a 2/2 creature with protection from green. The attacking creature’s controller must assign at least 2 damage to the blocker, even though that damage will be prevented by the blocker’s protection ability. The attacking creature’s controller can then choose to assign the rest of the damage to the defending player.
  • 502.9e When there are several attacking creatures, it’s legal to assign damage from those without trample so as to maximize the damage of those with trample.
    Example: A 2/2 creature with an ability that enables it to block multiple attackers blocks two attackers: a 1/1 with no special abilities a 3/3 with trample. The attacking player could assign 1 damage from the first attacker and 1 damage from the second to the blocking creature, and 2 damage to the defending player from the creature with trample.
  • 502.9f Multiple instances of trample on the same creature are redundant.

Trample is an ability generally printed on creatures with a large power, such as Crash of Rhinos or the ability to gain a large power, such as Keldon Battlewagon, and is generally seen on Green creatures, although all colours have fairly recently printed cards with it.