The word overall is also an adjective meaning "above everything".

An overall is usually used as protective clothing when working, but they have sometimes been items of fashion. Some people call an overall a "pair of overalls" by analogy with "pair of trousers".
There are two sorts of garment called an overall.

Bib-and-brace

These are trousers with an attached front patch covering the chest and with attached braces (U.S. suspenders) which go over the shoulders. Some people use the word "overall" for this garment only and not for a boilersuit.

Bib overalls are generally made of blue denim, and often have riveted pockets, similar to those of blue jeans. Bib overalls have long been associated with rural men in the U.S. South and Midwest, especially farmers. They are often worn with long_johns or a red union suit underneath, or with a t-shirt or no shirt at all in warmer weather. Since the 1960s, different colors and patterns of bib overalls have been increasingly worn by young people of both sexes, often with one of the straps worn loose or unfastened along the side and under the arm.

Boilersuit

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 and used as protective clothing at work. Its main feature is that it has no gap between jacket and trousers and no loose jacket tails. It often has a long thin pocket down the outside of the right thigh to put a ruler in. It usually has a front fastening extending the whole length of the front of the body up to the throat, with no lapels. This fastening can be:-

buttoned.

a zipper.

velcro, as nowadays in the British Royal Air Force (RAF).

popper buttons or press-studs.

They are often issued by factories to their workmen, with the firm's badge on it.
The French police unit called CRS use boilersuits as uniforms.
A dark blue coverall is the current working uniform of the U.S. Navy, with the owner's name and "U.S. Navy" on the chest, and rank insignia on the collar points.

Student overall

In Sweden and Finland, the students of universities and polytechnics wear special boilersuits. Typically, the overalls are procured by the student associations of faculties or major subject. The colour of the overall is usually characteristic of such association and, the subjects being many and colours few, also quite spectacular colours, as purple, turqoise or pink are used. In fact, the use of overalls is nowadays the most popular academic tradition despite its short history. The use of the overalls started in Swedish universities of technology in the late 1970's and spread quickly to Finland. The height of the use of the overall was reached in the late 1990's. Since then, the custom has been popular although perhaps in slight decline as the overalls are often viewed to signal a lifestyle bordering on alcoholism.

Unlike the overalls generally, the student overall is used only in parties and is, almost always decorated richly with badges and souveniers. Typically an overall will tell its owner's interests, political views, personal history and even military experience. There also exists a practice of swapping a part of the overall with a person with whom one has copulated. The intoxicated students roaming the city nights in their overalls wake mixed feelings but are an essential part of the night life in university towns. Traditionally, the use of overalls has been most widespread among the engineering students and the students of humanities have disdained their use, although even most of these do own a pair.