This is the term used to describe how fast a card effect is. All monster cards are Spell Speed 1. All Spell Cards are Spell Speed 1 except for Quick-Play Spells. All Traps and Quick-Play Spells are Spell Speed 2, except for Counter Trap Cards. Counter Trap Cards are the only cards that have Spell Speed 3.
Spell Speed 1 effects can't activate during the opponents turn or in a Chain to Spell Speed 2 Cards. Spell Speed 2 Effects can be used during the opponent's turn, but cannot chain to a Spell Speed 3 card. Spell speed 2 effects cannot activate during damage calculation. Spell Speed 3 effects can activate whenever their effect is applicable.