An acronym which stands for Never Again Volunteer Yourself. Popular among junior enlisted sailors when they are feeling especially bitter about the fact that they always have to strip and wax the 'deck' and clean the 'head'. Officers and senior enlisted (lifers) do not approve of this acronym or its usage.
The term is beginning to find some usage amongst the civilian population as well, usually after someone has volunteered him or herself to do something, only to have it turn into a giant pain in the ass that you can't get out of.
Regardless of the particular context, the term is always used while bitching about something.
Johnny: This sucks!!
Steven: Navy, dude. Navy.
Johnny: Yup. Navy.
You also sometimes hear it as a direct substitute for words like shitty, sucks, bullshit, etc.
Example: Johnny: This is so fucking Navy!!