I've been referencing the term "n-plied" with some of my yarn descriptions, and I thought I had better define what I mean.
N-plied: A shorthand term for navajo-plying, sometimes referred to as chain-plying. This plying technique takes a single strand of yarn and loops it back on itself before allowing plying twist to enter the chained section in order to create a 3-ply yarn . If you are familiar with crochet, the loops of yarn are very similar to creating a chain in crochet. Technically, this type of yarn is a not a true 3-ply yarn and does not have the same strength as a true 3-ply, but it otherwise behaves very similiarly. This technique is commonly used to maintain color repeats in a singles yarn. I use it for that purpose, and also for the times when I feel too lazy to rewind a singles yarn on to multiple bobbins for traditional plying.
If you're interested in learning more about navajo plying, I think the Yarn Wench's tutorial is one of the best explanations with both video & written instruction with photos. Also, the Yarn Harlot has a blog post from a few years ago that I think is a great summary of the pros & cons of n-plying.