Rather than a fixed number, some creature cards have power and/or toughness that includes a star (*).
June 17, 2011 · Commander 2011
An activated ability with a loyalty symbol in its cost is a loyalty ability. Loyalty abilities follow
April 1, 2011 · Duel Decks: Knights vs. Dragons
An activated ability with a loyalty symbol in its cost is a loyalty ability. Loyalty abilities follow special rules: A player may activate a loyalty ability of a permanent he or she controls any time he or she has priority and the stack is empty during a main phase of his or her turn, but only if none of that permanent's loyalty abilities have been activated that turn. See rule 606, "Loyalty Abilities."
February 4, 2011 · Mirrodin Besieged
An activated ability with a loyalty symbol in its cost is a loyalty ability. Loyalty abilities follow special rules: A player may activate a loyalty ability of a permanent he or she controls any time he or she has priority and the stack is empty during a main phase of his or her turn, but only if none of that permanent’s loyalty abilities have been activated that turn. See rule 606, “Loyalty Abilities.”
October 1, 2010 · Scars of Mirrodin
An activated ability with a loyalty symbol in its cost is a loyalty ability. Loyalty abilities follow
February 1, 2010 · Worldwake
An activated ability with a loyalty symbol in its cost is a loyalty ability. Loyalty abilities follow special rules: A player may activate a loyalty ability of a permanent he or she controls any time he or she has priority and the stack is empty during a main phase of his or her turn, but only if none of that permanent's loyalty abilities have been activated that turn. See rule 606, "Loyalty Abilities."