| Acronym | Meaning |
| MPY | Miles Per Year |
| MQC | Multiple-quantum Coherence |
| MQDT | Multichannel Quantum Defect Theory |
| MQED | Molecular Quantum Electrodynamics (calcn. Method) |
| MQES | Metastable-quenched Electron Spectroscopy |
| MQL | Method Quantitation Limit |
| MQL | Minimum Quantifiable Limit |
| MQMAS | Multiple-quantum Magic-angle Spinning |
| MQO | Measurement Quality Objective |
| MQW | Multiple Quantum Well |
| MR-ACPF | Multireference-averaged Coupled Pair Functional |
| MR-CCI | Multireference Contracted Configuration Interaction |
| MR-CEPM | Multireference-coupled Electron Pair Method |
| MR-CI-PS | Multireference-CI-perturbatively Selected |
| MR-L-CEPM | Multireference-linearized-coupled Electron Pair Method |
| MR-MBPT | Multireference-many-body Perturbation Theory |
| MR-MP | Multireference Moeller-Plesset (perturbation Theory) |
| MR-MP2 | Multireference Moeller-Plesset For Two-configuration Wave Function |
| MR-RWA | Many Resonance-rotating Wave Approxn. |
| MR-SAC | Multireference Symmetry-adapted-cluster (quantum Theory Or Wave Function For Mol. Calcns.) |
| MRA | Magnetic Resonance Angiography |
| MRA | Multiple Regression Analysis |
| MRAIRS | Multiple Reflection-absorption Infrared Spectroscopy |
| MRAM | Magnetic Random Access Memory |
| MRB | Multi-stage Reverse-flow Bioreactor |
| MRBW | Multireference Brillouin-Wigner |
| MRCC | Multireference Coupled Cluster |
| MRCEPA | Multireference Coupled-electron-pair Approxn. |
| MRCI | Multireference Configuration Interaction |
| MRD-CI | Multireference Determinant Configuration Interaction |
| MRD-CI | Multireference Double-excitation Configuration Interaction |
| MRDL | Maximum Residual Disinfectant Level |
| MRE | Mining Research Establishment |
| MRE | Metal Responsive Element |
| MRF | Material Recovery Facility |
| MRF | Magnetorheological Fluid |
| MRF | Municipal Recycle Facility |
| MRF | Myogenic Regulatory Factor |
| MRFM | Magnetic Resonance Force Microscope |
| MRI | Magnetic Resonance Imaging |
| MRINDO | Modified Rydberg Intermediate Neglect Of Differential Overlap |
| MRINDO/S | Modified Rydberg Intermediate Neglect Of Differential Overlap/spectral (or Screening) |
| MRIS | Municipal Refuse Incineration System(s) |
| MRISSA | Municipal Refuse Incineration System Simulation And Analysis Model |
| MRL | Maximum Residue Limit |
| MRL | Method Reporting Limit |
| MRL | Minimal Risk Levels |
| MRL | Minimum Reporting Level |
| MRLCC | Multireference Linearized Coupled Cluster |
| MRLV | Mobile Raman Lidar Van |