If you are choosing a knitting project you will notice that many patterns give you a rating of the perceived level of difficulty of the project. How this determination is made is often unclear.
As an example this info is from the Craft Yarn Council.
Skill levels for knitting
Projects for first-time knitters using basic knit and purl stitches.Minimal shaping.
Projects using basic stitches, repetitive stitch patterns, simple color changes, and simple shaping and finishing.
Projects with a variety of stitches, such as basic cables and lace,simple intarsia, double-pointed needles and knitting in the round needle techniques, mid-level shaping and finishing.
Projects using advanced techniques and stitches, such as short rows,fair isle, more intricate intarsia, cables, lace patterns, and numerous color changes.
You will notice that the descriptions above assume that you already know what is basic vs. advanced.
This is from knitty.com. (Look at the bottom of the page)
Suitable for beginners. Relaxing, not mentally taxing.
Fun things with zing. A twist, even. Friendly and unintimidating: very knittable by most knitters
A little something for the seasoned knitter. Daring but not exhausting. Probably not tv knitting.
Suitable for those with a lot of experience. Or patience. Or both. These babies have teeth. Hoo boy.
I love these descriptions for their humour but I'm not really any further ahead in my understanding.