Terminal differentiation refers to the process by which a cell becomes a specialized cell type and can no longer divide. Among the options provided, hair cells are a type of specialized cell that undergo terminal differentiation.
Epithelial cells, heart cells, and stem cells can undergo various stages of differentiation, but stem cells in particular have the capacity to differentiate into various cell types and can continue to divide. Therefore, the best answer in the context of terminal differentiation is:
hair cells.