The Collaborative International Dictionary of English v.0.48:

Bo \Bo\, interj. [Cf. W. bw, an interj. of threatening or
   frightening; n., terror, fear, dread.]
   An exclamation used to startle or frighten. [Spelt also boh
   and boo.]
   [1913 Webster]

The Free On-line Dictionary of Computing (19 January 2023):

bo

    The country code for Bolivia.

   (1999-01-27)