When partner opens one of a major suit and the responder has the values for game, it is valuable to distinguish between hands with distributional values, and hands with both trump support and all round strength (usually 13 to 15 points).
In the first case a direct raise to game, which has the additional value of having a pre-emptive effect, is in order. In the second case, bidding a second suit and then bidding game in partner’s opening suit at the next opportunity may better describe the hand – a delayed game raise.
For example:
With this hand, after partner opens 1♠, you respond 2♣ knowing you can bid 4♠ next time.
The use of splinters and 2NT as a game-forcing raise of partner’s major have made the delayed game raise less common than it once was.