A uniform is a variety of clothing worn by members of an organization while participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, security guards, in some workplaces and schools and by inmates in prisons.
Wearing an apron prevents your food coming into contact with the dust, dirt, hair, germs and whatever else might have been floating around you throughout your day. Finally, wearing an apron allows you to make a statement to those around you while you're cooking.
An overcoat is a type of long coat intended to be worn as the outermost garment, which usually extends below the knee. Overcoats are most commonly used in winter when warmth is more important.
Boilersuits are so called because they were first worn by men maintaining coal-fired boilers. To check for steam leaks or to clean accumulated soot from inside the firebox of a steam locomotive, someone had to climb inside, through the firehole