overall

This is sometimes called a coverall. In American English, it is nearly always referred to as "coveralls". It is a one-piece garment with full-length sleeves and legs like a jumpsuit, but usually less tight-fitting. Its main feature is that it has no gap between jacket and trousers or between lapels, and no loose jacket tails. It often has a long thin pocket down the outside of the right thigh to hold long tools. It usually has a front fastening extending the whole length of the front of the body up to the throat, with no lapels. It may be fastened with buttons, a zipper, velcro, or snap fasteners. Boilersuits with an attached hood are available. The word "boilersuit" may also refer to disposable garments such as Dupont's Tyvek suits.
Boilersuits are so called because they were first worn by men maintaining coal-fired boilers. In order to check for steam leaks or to clean accumulated soot from inside the firebox of a steam locomotive, it is necessary for someone to climb inside, through the firehole (where the coal is shovelled in). A one-piece suit avoids the potential problem of loosened soot entering the lower half of the cleaner's clothing through the gap in the middle. As the firehole opening is only just large enough for a fit individual to negotiate, a one-piece suit also avoids the problem of the waistband snagging on the firehole as the person bends to wriggle through.
Uses of boilersuits
Coveralls are most often worn as protective clothing over "street" clothes at work. They are sometimes also worn directly over shirt and underclothes.
Coveralls called student overalls are used by university students in some Scandinavian countries as a sort of party-uniform, with insignia on the back and color varying with program and university. It is also practice to customize the coverall in a variety of ways, including adding a large number of patches, and exchanging parts of the suit with other students.