Mohair weft is mohair that has been sewn together at the top of the lock into a continuous strip . This allows it to combed and either sewn to a wig cap or can be crocheted along while creating a cap, see here
Wefts are washable and may be combed. All the wefts sold are single sewn wefts.
Lali Doll Nursery have tutorials for handmade wefted doll wigs: