Volunteering
A volunteer is someone who helps a common cause and who does not expect to get paid for it. There are many cases, such as cleaning up after a disaster, where anyone can help. There are many cases, though, where the volunteers are trained specialists. Examples for these are the volunteer fire departments or a doctor or nurse working for organisations such as the Red Cross. Another example are the people guiding police dogs, which may be trained for emergency rescue.
Volunteering Media
Volunteers of Vilnius Marathon
Volunteers sweep the boardwalk in Brooklyn after the 2012 Hurricane Sandy
Semi-professional volunteering: Trained lifeguards of the German DLRG, the largest voluntary water rescue organization in the world, patrolling a public bathing area of a lake in Munich
John F. Kennedy greets volunteers on 28 August 1961
Some files for helping people in a volunteers station in Shenzhen, People's Republic of China