A Wife, Fiancé, or Serious Girlfriend of a U.S. Marine.
A Female Most men find Stunning, Usually a Woman who can have any guy she wants, but remains Completely faithful to her significant other/Spouse while He's away in the Marines Corps.

The horrible moment when you realise that you have accidentally done something very slightly wrong which has very bad (usually embarassing) implications for you. This is typically the moment of realisation that you just sent a dirty text message to a close member of family, typically your mother, rather than the intended recipient.