It’s the name given to whatever combination of rope and chain runs from your boat to the anchor. It’s also called the anchor cable. Chain is strong and resists all kinds of abrasion under water, but it doesn’t absorb shock. If the wind gets up and you have all chain, you’ll get jarring through the boat as the chain reaches its full length. A length of strong rope (usually triple-strand nylon) has a degree of stretch, so it acts as an effective shock absorber. If you buy a boat anchor kit, you’ll get both.