The use of the simple cue bid, ie a direct overcall in the suit opened by an opponent (as in the sequence 1♣-2♣ or 1♠-2♠), to show a two-suited hand. The cue bid over a minor-suit opening shows both majors while the cue bid over a major-suit opening shows the other major and a minor suit.
After the overcaller shows both majors, advancer normally shows preference, jumping if appropriate. After the major/minor cue bid, if advancer does not have support for the major, it is usual to play 3♣ as ‘pass or correct’ while 2NT is an enquiry with a stronger hand. The original convention admitted hands with 5-4 shape but the modern style demands at least 5-5. Some partnerships allow the cue bid on weak or strong hands (but not those with intermediate strength) while others allow it on any hand with sufficient values to bid and the right shape.
Here is the Michaels Cue Bid in action: