Untrample is a slang term for the ability of creatures to assign their combat damage to target creature instead of defending player when they aren't blocked. It first appeared in Fallen Empires.
Examples
Example
Zealot il-Vec 
Creature — Human Rebel
1/1
Shadow (This creature can block or be blocked by only creatures with shadow.)
Whenever Zealot il-Vec attacks and isn't blocked, you may have it deal 1 damage to target creature. If you do, prevent all combat damage Zealot il-Vec would deal this turn.
Color percentages
There is a total of 6 cards that involve untrample, which divide by color as such:
- 50%
33%- 17%
Cards with untrample
Creatures with untrample
Spells that grant untrample