XO

symbol for the karyotype in which there is only one sex chromosome, an X chromosome, the other X or Y being absent; it is observed in most cases of Turner syndrome.
Found on http://www.encyclo.co.uk/local/21001

Xo

XO is an abbreviation for Executive Officer
Found on http://www.probertencyclopaedia.com/N24.HTM

XO

Executive Officer, the second in command of a unit, known as a Chief of Staff for a general.
Found on http://www.translationdirectory.com/glossaries/glossary119.htm

XO

eXecutive Officer
Found on http://www.translationdirectory.com/glossaries/glossary125.htm

XO

Executive Officer
Found on http://en.wikipedia.org/wiki/List_of_U.S._government_and_military_acronyms
No exact match found