The Collaborative International Dictionary of English v.0.48:

Quo warranto \Quo` war*ran"to\ (kw[=o]` w[o^]r*r[a^]n"t[-o]).
   [So called from the Law L. words quo warranto (by what
   authority), in the original Latin form of the writ. See
   Which, and Warrant.] (Law)
   A writ brought before a proper tribunal, to inquire by what
   warrant a person or a corporation acts, or exercises certain
   powers. --Blackstone.
   [1913 Webster]

   Note: An information in the nature of a quo warranto is now
         common as a substitute for the writ. --Wharton.
         [1913 Webster]

WordNet (r) 3.0 (2006):

quo warranto
    n 1: a hearing to determine by what authority someone has an
         office or franchise or liberty

Bouvier's Law Dictionary, Revised 6th Ed (1856):

QUO WARRANTO, remedies. By what authority or warrant. The name of a writ
issued in the name of a government against any person or corporation that
usurps any franchise or office, commanding the sheriff of the county to
summon the defendant to be and appear before the court whence the writ
issued, at a time and place therein named, to show "quo warranto" he claims
the franchise or office mentioned in the writ. Old Nat. Br. 149; 5 Wheat.
291; 15 Mass. 125; 5 Ham. 358; 1 Miss. 115.
     2. This writ has become obsolete, having given way to informations in
the nature of a quo warranto at the common law; Ang. on Corp. 469; it is
authorized in Pennsylvania by legislative sanction. Act 14 June, 1836. Vide
1 Vern. 156; Yelv. 190; 7 Com. Dig. 189; 17 Vin. Ab. 177.
     3. An information in the nature of a quo warranto, although a criminal
proceeding in form, in substance, is a civil one. 1 Serg. & Rawle, 382.