TRAP

The most common usage is against strong Club systems such as Precision.

These are direct overcalls of any strong 1♣! openings:

Double                     Shows a Heart suit. 5+ cards
1♦                           Shows a Spade suit. 5+ cards
The next three are CRM style:
1♥                           Shows two suits, either both red or both black 4-4 or better
1♠                           Shows two suits, either both Majors or both minors 4-4 or better
1NT                         Shows either Clubs & Hearts OR Diamonds & Spades 4-4 or better
The next  four bids show either a 6 card in the NEXT suit OR both the two suits after that:
2♣                           Shows 6+ Diamonds OR both Majors 5-5
2♦                           Shows 6+ Hearts OR both black suits 5-5
2♥                           Shows 6+ Spades OR both minors 5-5
2NT                         Shows 6+ Clubs OR both red suits 5-5
Other bids are found in other texts but the above is sufficient.

In all of the above responder relays with the next suit - If and only if  the RHO passes