When a guy is obsessed with a girl and collects her individual hairs that have fallen out to comprise a "hair doll".
The guy collects enough hair to make a small person/figure out of hair.
The name of the hair doll can simply be "Hair Doll" or often is named after the girl being stalked. Also, prefixes are often added to the girls name. For example, if the girls name is Molly, the name of the hair doll could be Lil' Molly or Miss Molly.