See also: Appendix:Variations of "er"
- Abbreviation of Elizabeth Regina. (Queen Elizabeth)
- (physics) Abbreviation of Einstein-Rosen bridge.
ER (plural ERs)
- (baseball) The statistic "Earned Run" (a run that was scored without the aid of an error by the fielding team that is charged to the pitcher responsible for allowing the runner that scored to reach base.)
- (biology) Initialism of Endoplasmic Reticulum.
- (computing) Initialism of Entity-Relationship.
- (medicine) Initialism of emergency room.
- (computing): EER
- (sports) Abbreviation of Erie.