Basal surface

Definition
noun
(histology) The edge of the cell or tissue facing the underlying connective tissue
(dentistry) The impression surface of denture
Supplement
In histology, the basal surface is the bottom edge of the cell or tissue adjacent to the basement membrane. In particular, the epithelial tissue is a group of cells (called epithelial cells) that lie together to carry out a common function. The epithelial tissue acts as a covering. It lines cavities in the body and the surfaces of structures. Its other functions are for secretion, selective absorption, protection, transcellular transport, and sensation. Underneath the epithelial tissue is a thin, fibrous, non-cellular region of tissue called basement membrane to separate the epithelial tissue from the underlying connective tissue. The basement membrane acts as an anchorage between the epithelial tissue and the connective tissue. It is also through it that the epithelial layers receive nourishment. Substances from the connective tissue passes through the basement membrane to reach the epithelial tissue.¹ The bottom edge of the epithelial tissue next to the basement membrane is the basal surface. In contrast, the edge of the epithelial tissue facing the lumen or the external environment is called the apical surface. ²
In dentistry, the basal surface of a denture pertains to the part of the denture base shaped to fit to the basal seat for the denture.
Reference(s):

¹ Eurell, Jo Ann C. et al., eds. (2006). Dellmann’s textbook of veterinary histology. Wiley-Blackwell.

² Tamarkin, D. A. (2011). Epithelial Tissue. Retrieved from ://faculty.stcc.edu/AandP/AP/AP1pages/Units1to4/epitissmol/epitheli.htm Link