I keep hearing those soldiers in the game Call of Duty: Modern Warfare 2 use the term "Oscar Mike". As in, "We are Oscar Mike", "Squad/ fire team is Oscar Mike", and "Tango is Oscar Mike".
What's this? So I googled it up. Apparently, it means being "on the move". The military abbreviation for "On the Move", it seems, is "OM". And in NATO phonetics "O" is "Oscar" and "M" is "Mike", so "OM" would be "Oscar Mike".
Sounds like this term got famous after having been featured in the drama Generation Kill.
Interesting. At least, I can now concentrate on what's actually happening instead of wondering what that means:-)