2/1, 3/1, 2/2 etc.
Woven fabric consists of warp and weft yarns crossing each other one at a time or in groups. Plain weave always consists of one warp yarn crossing one weft yarn, a 1/1 weave. When two warp yarns cross a weft yarn, this can be indicated as 2/1 weave. 2/2 weave has two warp yarns crossing two weft yarns.
These fractions are read, for example, “three up, one down” for 3/1, indicating that three weaving harnesses are raised, then one is lowered for three warp yarns on the face, then one weft yarn.
See also Weaving
A satin weave is most commonly 4/1 with warp yarns floating over weft yarns in numbers of 4 to 1, but can be 7/1 and even 11/1, and the interlacings do not occur in rows, giving the most uninterrupted gloss possible.
One of the more jaw-dropping satin dresses I’ve had a chance to see up close is this Ceil Chapman ball gown currently in my web store. The fabric really defines “pour of satin.”