The Collaborative International Dictionary of English v.0.48:

Om \Om\, interj. & n. [Also Aum, Um.] [Skr. [=o]m.]
   A mystic syllable or ejaculation used by Hindus and Buddhists
   in religious rites, -- orig. among the Hindus an exclamation
   of assent, like Amen, then an invocation, and later a symbol
   of the trinity formed by Vishnu, Siva, and Brahma.

   Om mani padme hun, a sacred formula of buddhism (esp. of
      the Lamaists) translated "O, the Jewel in the Lotus,
      Amen," and referring to Amitabha, who is commonly
      represented as standing or sitting within a lotus.
      [Webster 1913 Suppl.]

The Free On-line Dictionary of Computing (30 December 2018):

om

    The country code for Oman.

   (1999-01-27)