Removal is a spell or ability that is used to remove permanents from play permanently, either by putting the permanent in the graveyard or by exiling it, or any other place that the creature cannot return from. Removal is the most common type of answer to permanents other than the blocking of attacking creatures.
Commonly removal means one of six effects: 
- Effects that destroy the permanent, such as Doom Blade or Naturalize.
- Effects that can deal damage to a creature, such as Lightning Bolt.
- Effects that can reduce a creature's toughness, such as Last Gasp.
- Effects that exile a permanent, such as Swords to Plowshares. 
- Effects that force the permanent's controller to sacrifice it, such as Cruel Edict.
- Effects that move (tuck) the creature to a generally inaccessible place, such as Bant Charm.