| Acronym | Definition |
|---|
| ER | Emergency Room |
| ER | Extended-Release |
| ER | Earned Runs (baseball; pitching) |
| ER | Error |
| ER | Entity Relationship |
| ER | Energy Research |
| ER | Employer (IRB) |
| ER | Emergency Response |
| ER | Office of Energy Research |
| ER | Estrogen Receptor |
| ER | Extended Range |
| ER | Extended Range (C-17 acquisition program) |
| ER | Enterprise Resource Planning |
| ER | Early Release |
| ER | Event Registration |
| ER | Eastern Region |
| ER | Educational Research |
| ER | Eritrea |
| ER | Employment Relations |
| ER | Employee Relations |
| ER | Easy Rider (movie) |
| ER | External Relations |
| ER | Evaluation Report |
| ER | Early Retirement |
| ER | Environmental Restoration |
| ER | Electromagnetic Radiation (energy) |
| ER | Environmental Report |
| ER | Entre Rios (Argentina Province, airline code) |
| ER | Emission Reduction (environment) |
| ER | Electronic Records |
| ER | Erbium |
| ER | Equipment Required |
| ER | Endoplasmic Reticulum |
| ER | Earth Resources |
| ER | Extensive Reading |
| ER | Event Rate |
| ER | Energy Rating |
| ER | Eleanor Rigby (Beatles song) |
| ER | Eye Relief (optics) |
| ER | Equipment Room |
| ER | Escape Route |
| ER | Expense Ratio |
| ER | Ecosystem Restoration |
| ER | Educational Researcher (journal) |
| ER | Evidence Rule |
| ER | Employee Retention |
| ER | Epic Records (record label) |
| ER | Exceptional Release (mission capable aircraft) |
| ER | Enfermedad Rara (Spanish: Rare Disease) |
| ER | Ecological Reserve |
| ER | Electron Reflectometer |
| ER | Electrical Resistivity |
| ER | Excerpts of Record (legal documents) |
| ER | Eastern Railway |
| ER | External Rotation |
| ER | Evolutionary Robotics |
| ER | Expenditure Request (various organizations) |
| ER | Emotional Rescue (Rolling Stones album) |
| ER | Expense Report |
| ER | Evening Reading (Shacknews) |
| ER | Elektra Records (record label) |
| ER | Employer's Requirements |
| ER | Energy Resolution |
| ER | Enhancement Request |
| ER | Engineering Report |
| ER | Earnings Record |
| ER | Exchange Ratio |
| ER | Explicit Routing |
| ER | Explicit Rate (networking) |
| ER | Established Record |
| ER | Expanded Response |
| ER | Energy Regulator |
| ER | Electro-Rheological |
| ER | Engineroom |
| ER | Enterprise Requirements |
| ER | Enhanced Radiation |
| ER | Engineer Regulation |
| ER | Efficiency Review |
| ER | External Resistance |
| ER | Established Reliability (C-17 acquisition program) |
| ER | Employee Request |
| ER | Equilibrium Reactions |
| ER | Engineering Release |
| ER | Electronic Reconnaissance |
| ER | Efficient Review |
| ER | Extracellular Release |
| ER | Ephemeral Region |
| ER | Electricity Report |
| ER | Echo Ranging |
| ER | Enantiomeric Ratio (chemistry) |
| ER | Electoral Region (UK) |
| ER | Engineering Request |
| ER | Estimate of Repair |
| ER | DHL Airways, Inc (IATA airline code) |
| ER | Enhancement Report |
| ER | Euro Repuestos SA (Guatemala) |
| ER | Effective Roughness |
| ER | Eternal Rage (Call of Duty gaming clan) |
| ER | Executive Registrar |
| ER | Equipment Requisition |
| ER | Extracting Roots |
| ER | Elizabetha Regina (Queen Elizabeth) |
| ER | Error Recorder |
| ER | End Transaction and Retrieve |
| ER | Electronic Requirement |
| ER | Exploitation Requirement |
| ER | Elite Regions (Ominix gaming) |
| ER | Enceinte Réacteur (French: Reactor Chamber) |
| ER | Electrolytic/Electrochemical Refining |