Historical Rules · 27 March 2015
Rule 701.4a
Official source text from the 27 March 2015 Rules release
To cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if he or she has priority. See rule 601, “Casting Spells.”