Every distinct wording since 2010, newest first.
July 12, 2019 · Core Set 2020
An instant or sorcery spell is targeted if its spell ability identifies something it will affect by using the phrase “target [something],” where the “something” is a phrase that describes an object and/or player. The target(s) are chosen as the spell is cast; see rule 601.2c. (If an activated or triggered ability of an instant or sorcery uses the word target, that ability is targeted, but the spell is not.)
February 1, 2010 · Worldwake
A player may cast an instant spell any time he or she has priority. A player may cast a noninstant spell during his or her main phase any time he or she has priority and the stack is empty.