I've seen the following:
When using this esoteric metric what abbreviation is most commonly used?
I've always just seen:
I've always known it to be SLOC - Source Lines Of Code.
That is assuming you only care about the actual code. If you're taking whitespace and comments into consideration (I'd ask why, but then again, we're already talking about lines of code as a metric...) then SLOC wouldn't be the right term.