Intermediate Chess Lessons: Queen and King Checkmate

What is checkmate? – ICC

Chess: Can you checkmate with three queens against a lone king?

How Can You Checkmate in Two Moves with a Queen and King in Chess

Checkmate. Queen Check The King In A Chessboard by Stocksy

Classic Chess (King, Queen, Checkmate). Art Print by Happy go ella

Chess, game, strategy, winner, checkmate, queen, gambit icon

Chess Endgame: King and Queen vs. King and Knight

Chess Pieces Pawn King Queen Checkmate Strategy Gift Acrylic Print by Thomas Larch - Fine Art America

Checkmate Puzzle

In this position, (black to move) Qe1 is apparently checkmate, but I am confused because the rook is pinned and therefore cannot defend the queen. Can someone explain this to me?