What qualifies as an institution of Purely Public Charity?

The institution must be a nonprofit, public charity.  Private charity does not qualify.  Purely public charity is described as whatever is done or given gratuitously in relief of public burdens or for the advancement of public good.  Where the public is the beneficiary, the charity is public.  And where no private or pecuniary return is reserved to the giver or to any particular person, but all the benefit resulting from the gift or act goes to the public, it is a purely public charity; the word ‘purely’ being equivalent to wholly.