A fireman is someone whose job is to put out fires and keep people safe. They work with heavy equipment and are trained to deal with emergency situations.
You might see or hear about firefighters on TV, but in real life, they're just like regular guys who happen to be really brave and strong. Their job is not only to fight fires, but also to help people get out of burning buildings and stay safe until the fire is put out. Firemen often work together as a team, so you might see them wearing matching uniforms and helmets with a big "FD" or department logo on it.
Someone (especially one who is male) who is skilled in the work of fighting fire.
