Core sheath spinning refers to spinning a yarn that consists of two different polymers. The polymers are however not mixed (like it is with co-polymer yarns). Rather, one polymer is in the core situated while the other polymer is coated around the core, functioning as a sheath.
Core sheath spinning is mostly done by melt spinning whereas it is very seldom to also find a core-sheath-yarn spun by other spinning techniques like wet spinning.
The advantage of core sheath yarn is that the yarn has characteristics of both polymers. For example, the polymer of the sheath can have a lower melting temperature than the polymer in the core: an ideal prerequisite for adhesion melting.