This is a form of takeout double.
A negative double is only used after your partner has opened and has been overcalled. The maximum level at which a negative double is used is determined by partnership agreement.
To use a negative double the responder must have at least 6 points and a four card unbid major suit.
If the bidding has reached the two level then the responder should have at least 8 points when using a negative double e.g. 1D- 2C - DBL
The opener must rebid. The opener can rebid normally in the knowledge that the responder has at least 6 points and a four card major suit.
There is no maximum point count (unless agreed) for a negative double. The responder can show a stronger hand in the next round of bidding.
If both majors have been bid then a negative double shows both minors.
A negative double can also be used when the responder has a weak hand with a long major suit and doesn't want to bid at two level but wants to show the major.