Last width on a ski boot means the ski boot’s shape and width inside the shell or the outer boot area. If you have a narrow foot, then a narrow width of about 97-98mm last range should fit you well. Medium feet will most likely measure into the 100-102mm last width area, and those with wide feet need a last width of 102mm and up.
If you have a narrow foot or want a boot that will fit snugly to enhance performance, then a narrow last width ski booth will work well for you. These boots also tend to be low in volume overall. Most skiers find that medium lasted boots are more comfortable since they fit the more standard foot sizes. However, if you have wide feet or want extra space in your boot, then a wide last width booth might be better for you.
The type of last width you decide upon will depend a lot on your skill level and how narrow or wide your foot really is. In many ways, this feature is important, but it’s also a matter of personal preference, so it’s best to try on the ski boots to see how comfortable the last width is for you before you purchase a pair.