Nail pitting is when numerous small, pinpoint-like depressions and a perforated appearance form on the surface of the nail. This name comes from the resemblance of these numerous small depressions (pitting) on the nail's surface to the perforated, textured structure of a traditional sewing thimble. This appearance is usually a reflection of damage in the nail matrix (its root). It's most commonly associated with psoriasis, but can also be seen in alopecia areata, eczema and certain autoimmune conditions.
This type of surface irregularity in the nail can be a sign of an underlying systemic condition. Dermatological assessment is important for diagnosis and treatment.