5NT can mean the following: * After a 1NT or 2NT opening, 5NT is usually an invitation to 7NT, asking opener to bid 6NT if minimum and 7NT is maximum. * After Blackwood 4NT and a response, 5NT is asking for kings. * After Gerber 4♣ and 5♣, 5NT shows 3 kings. * As a voluntary jump bid, 5NT is often Grand slam force. * After a sequence of control-showing cue-bids, 5NT is often used for trump ask. 5NT is very rarely a signoff and is the least commonly played contract in bridge.