First strike
From M:TG Archive, a library of Magic: The Gathering information
First strike is a core keyword ability. It has appeared in every Magic: The Gathering set. The ability is mainly red and white, such as in the card 'White Knight'.
Creatures with first strike deal combat damage before creatures without first strike. A separate first strike damage step is created for these creatures. For example, a 3/1 creature with first strike that is blocked by a 2/2 creature without witll deal 3 damage to the 2/2 creature, which destroys that creature before it can deal its damage to the first strike creature. Thus, the 3/1 creature with first strike will survive combat.
A related ability, double strike, also uses the first strike damage step.