What is satin weave fabric? How is it different from satin as a fibre?

This is one of the most common confusions in fabric terminology — "satin" describes a weave structure, not a fibre type:

Satin weave (the construction):

• One of the three fundamental weave structures (along with plain weave and twill weave)
• In satin weave, warp threads float over many weft threads before interlacing — creating long floats on the fabric surface
• The long floats reflect light uniformly — creating the characteristic smooth, glossy surface
• The reverse side is dull

Satin fabrics — the fibre can vary: