Final answer:
The skin surrounding the nail on three sides is known as the cuticle or eponychium. It protects the nail plate and prevents infection.
Step-by-step explanation:
The tissue or skin that surrounds the nail on three sides is called the cuticle, also known as the eponychium. The cuticle is a fold of epithelium that extends over the nail bed. It serves as a protective barrier to seal the edges of the nail plate and prevent infection in the underlying tissues. The nail fold is located at the sides and the proximal end of the nail, which overlaps with the nail body, helping to anchor it in place.