The s-orbital is a type of atomic orbital that can hold a maximum of two electrons. It is spherical in shape and is the simplest of all orbitals. Each energy level in an atom has one s-orbital, starting from the first energy level, where the 1s orbital is found. In the context of quantum mechanics, the s-orbital is described by a set of quantum numbers that define its size and energy. The presence of s-orbitals is crucial for understanding the electron configuration of elements in the periodic table, influencing their chemical properties and bonding behavior.