The Northern California Fly Fishing Board

I was reading an article on steelheading, and I came across a term that refers to the loop of loose fly line between your reel and hand when you're swinging a fly. In the past, I always had to use a sentence or two to describe it.

The article calls it the "loop slip". I'm not exactly sure how to use it in a sentence, but I think it's a noun.

Has anyone else heard this term before? It didn't sound like something the author merely created for the article.