What was the Northwest Passage and why were the French, Dutch, and English explorers looking for it?

It might be said that European explorers wanted "to find a trade route from the Atlantic to the Pacific ocean (Northwest Passage). The first ones who looked for it were John Cabot, an Italian sailor who explored for the King of England. Cartier Da Verrazano (French) and Henry Hudson (Dutch) however, none of them could find it