WAEC - Chemistry (2024 - No. 33)

Pairs of outermost shell electrons that are not used in bonding are called lone pairs or non-bonding pairs. 

A lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bond and is sometimes called an unshared pair or non-bonding pair. Lone pairs are found in the outermost electron shell of atoms.