lone (electron) pair

https://doi.org/10.1351/goldbook.L03618
Two paired electrons localized in the @V06588@ shell on a single atom. Lone pairs should be designated with two dots. The term 'nonbonding electron pair' is more appropriate, and is found in many modern text books.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1137 [Terms] [Paper]