Atk is a parameter that describes the ATK of a card.

Acceptable forms:

Atk:300   ---exactly 300 ATK

Atk:>300   ---greater than 300 ATK

Atk:>=300  --greater than or equal to 300 ATK

Atk:<300    ---less than 300 ATK

Atk:<=300   ---less than or equal to 300 ATK

Atk!:300    ----NOT 300 ATK

Spell and Trap cards (except Trap Monsters, etc.) will always test False for any of the above forms.

Also see OriginalAtk