A subshell is the set of orbitals within a shell that share the same principal quantum number n and the same angular momentum quantum number l. The subshells are labelled s, p, d, and f, according to the value of l. For example, the 3d subshell consists of the five d orbitals in the third shell.

亚层是壳层中具有相同主量子数 n 和相同角动量量子数 l 的一组轨道。亚层按 l 的取值标记为 s、p、d、f。例如,3d 亚层由第三壳层中的五个 d 轨道组成。