Tilt at windmills

What does the phrase "to charge off to tilt at windmills" mean?

It means attacking imaginary enemies, Thierry. The image is from 'Don Quixote' by Miguel Cervantes; if I remember correctly, DQ thought the blades of a windmill were dragon wings and charged at them on horseback to attack them with his lance. 'Tilt' here has a special meaning from medieval tournaments. I'm open to correction but I think it involved charging on horseback at an opponent or a target with the intention of hitting them with your lance.