Pro bono

Etymology

Short for the Latin pro bono publico, "for the public good," from pro, "for," bonum, "good," and publicum, "public." The phrase names work undertaken for the common benefit rather than for a fee. It is most strongly associated with the legal profession’s tradition of free representation.

adverb · /proh-BOH-noh/
Done professionally and without charge, especially legal work for those who cannot afford it.
What it names
The unpaid hours many law firms expect their lawyers to give to clients and causes that could never pay the usual rates.
Example
She took the eviction case pro bono, knowing the tenant could not have paid a cent.
Related idea
Pro bono work is given free for the public good; an amicus curiae brief is often filed pro bono too, but is a specific way of assisting a court rather than a client.