Definition - What does Pro Bono mean?
Pro bono is a shortened form of the Latin term "pro bono publico" which means "for the public good." In common usage, the term refers to taking on voluntary professional work without any compensation or at a reduced fee for the public good. Pro Bono differs from volunteerism. It specifically signifies voluntary work undertaken by a professional. This term is most often used to refer to lawyers who take on a case without compensation.
Justipedia explains Pro Bono
When a professional such as a lawyer or doctor undertakes work for free or at a reduced rate, it's called pro bono service. Many bar associations fix a mandatory number of hours that a lawyer must work pro bono in a year. Pro bono service is an important medium through which legal aid is provided to needy individuals.