Source : Webster's Revised Unabridged Dictionary (1913)

Informality \In`for*mal"i*ty\, n.; pl. {Informalities}.
   1. The state of being informal; want of regular, prescribed,
      or customary form; as, the informality of legal
      proceedings.

   2. An informal, unconventional, or unofficial act or
      proceeding; something which is not in proper or prescribed
      form or does not conform to the established rule.

Source : WordNet®

informality
     n 1: a manner that does not take forms and ceremonies seriously
          [ant: {formality}]
     2: freedom from constraint or embarrassment; "I am never at
        ease with strangers" [syn: {ease}]