A sequence such as 1♣-1♠, where responder bids at the one-level. A one- over-one response has a very wide range and (by an unpassed hand) is forcing for one round. Responder may have as few as 5 or 6 points or, with an unsuitable hand type for a jump shift, great strength.
A one-over-one response of 1♠ is correct with either of the above hands if partner opens one of either minor.