It's not check but the next move is checkmate I have 5 pieces left and my opponent only has his king. It is my opponent's turn and his king is not in check but everywhere his king moves is checkmate. Who wins?
If it is your opponent's turn to move and none of your opponent's pieces can move other than his king, and the king would be in check on any square it could move to, we would call that stalemate.
In case of stalemate, neither player wins – the game is drawn.

Here are a few examples:


A simple one with just 3 pieces on the board with Black to move:




Here, the black king has nowhere to go, the squares h8, h7, g7 and f8 are controlled by the white queen and f7 is controlled by the white king. 




Another position of stalemate with a few more pieces on the board, again with Black to move:




Black has 2 pawns and his king. His pawns can’t move forward or capture any pieces and his King can’t move anywhere as its surrounding is controlled by the pieces as shown in the image.




A little more complicated one with even more pieces on the board (white to move):




Positions like this one occur only very rarely! I believe it is a composition by someone and hasn't occurred in a real game.
Here all the pieces are on the board and yet White has no moves to make. All his pawns are fixed, most of his other pieces are blocked by his own pieces and the only 3 pieces which have space to move are the rook on g3, the knight on d2 and the king on e1. None of these three pieces can move since that would leave the king in check! Unfortunately this is a draw, because it is a stalemate.