A tarpaulin is a heavy, waterproof piece of fabric that's used as a protective cover or shelter. You might drape a tarpaulin over your tent when it starts raining in the middle of your camping trip. Or you can just go home.
Tarpaulins are often called tarps for short. The word probably includes tar because of the original method for waterproofing a tarpaulin, which involved spreading tar on a heavy piece of canvas. The pall part means "cloth." During the 19th century, it was common to abbreviate the word as paulin, especially in nautical terminology.