This is woolen yarn NM 15/3.

This tells the thickness/weight of the yarn,  as well as how many threads are combined.

3 threads twisted firmly so the volume is not too big and the strentgh optimal. Ideal for sewing.

Due to this strong twist we do not recommend this yarn for weaving.

Classic fabrics is getting more and more different thicknesses and a good way to keep them apart is this NM.

Another good way to understand the weight is to compare them all with how many meters go in one gram of yarn. All this info you can find at the specifications.