in human anatomy, "cuticle" can refer to several structures, but it is used in general parlance and even by medical professionals when speaking with patients to refer to the thickened layer of skin surrounding fingernails and toenails (the eponychium) and to refer to the superficial layer of overlapping cells covering the hair shaft (cuticula pili) that locks the hair into its follicle, consisting of dead cells. it can also be used as a synonym for the epidermis, the outer layer of skin.