Source : Webster's Revised Unabridged Dictionary (1913)

Public-service corporation \Public-service corporation\ or
   sometimes Quasi-public corporation \Quasi-public corporation\
   A corporation, such as a railroad company, lighting company,
   water company, etc., organized or chartered to follow a
   public calling or to render services more or less essential
   to the general public convenience or safety.

Source : WordNet®

public-service corporation
     n : a company that performs a public service; subject to
         government regulation [syn: {utility}, {public utility}]