A quantity of yarn, thread, etc. put up together in an oblong shape, after it is taken from the reel. A skein of cotton yarn is formed by eighty turns of the thread around a fifty-four inch reel.
(figuratively) A web, a weave, a tangle.
(zoology) The membrane of a fish ovary.
(wagonmaking) A metallic strengthening band or thimble on the wooden arm of an axle.
(zoology, UK, dialect, collective) A group of wild fowl (e.g. geese, goslings) when they are in flight.
(sports) A winning streak.
(radio, television, dated) A series created by a web (major broadcasting network).
In my experience a skein is a specific type of wound wool. It's looped and then twisted and folded over. You can't knit from a skein, you have to reball it first.