In competitive sequences, responder cuebids an opponent's bid to show a limit raise or better in opener's major. Also used on defense. A jump raise in competition is therefore preemptive.
1H - (2C) - 3C = show heart support and at least
3H = Pre-empt.
I prefer to use it after our side overcalls. Cuebids of opponent's suit now show a good raise or GF.
(1H) - 1S - (Pass/1NT/2C/2D) - 2H = Good raise in spade OR GF.