| Acronym | Meaning |
| MLK | Mixed-lineage Kinase |
| MLOPEX | Mauna Loa Observatory Photochemistry Experiment |
| MLPCA | Maximum Likelihood Principal Component Analysis |
| MLR | Multilinear Regression |
| MLRA | Multiple Linear Regression Analysis |
| MLS | Microwave Limb Sounder |
| MLS | Molecular Luminescence Spectroscopy |
| MLSC | Microvolume Laser Scanning Cytometry |
| MLSCN | Molecular Libraries Screening Centers Network |
| MLSS | Mixed Liquor Suspended Solids |
| MLT | Magnetic Local Time |
| MLTCS | Mesosphere-lower Thermosphere Coupling Study |
| MLVA | Multiple-locus Variable-number Tandem Repeat Analysispar |
| MLVSS | Mixed Liquor Volatile Suspended Solids |
| MM | Misch Metal |
| MMA | Manual Metal Arc Welding |
| MMA | Methyl Methacrylate |
| MMAD | Mass Median Aerodynamic Diameter (aerosol) |
| MMC | Metal-Matrix Composite |
| MMC | Molecular Mechanics For Clusters Model |
| MMCDF | Multichannel Multiconfiguration Dirac-Fock Method |
| MMD | Mass Medium Diameter (particle Size) |
| MMDR | Microwave-microwave Double Resonance |
| MMEF | Maximum Mid-expiratory Flow (lung Function) |
| MMFF | Molecular Mechanics Force Field |
| MMI | Mucous Membrane Effects |
| MMI | Man-machine Interface |
| MMIC | Monolithic Microwave Integrated Circuit |
| MMLV | Moloney Murine Leukemia Virus |
| MMMF | Man-Made Mineral Fiber |
| MMO | Mixed-mode Oscillation |
| MMP | Monitoring Master Plan (of North Sea Task Force) |
| MMP | Matrix Metalloproteinase |
| MMPC | Metal-matrix Particulate Composites |
| MMR | Magnetometric Restivity (method For Subsurface Characterization) |
| MMR | Mismatch Repair |
| MMS | Merged Markush Service |
| MMS | Molecular Modulation Spectroscopy |
| MMSE | Minimum Mean Square Error |
| MMSV | Morse-Morse-Spline-van Der Waals (potential Function) |
| MMT | Methylcyclopentadienylmanganese Tricarbonyl |
| MMTV | Mouse Mammary Tumor Virus |
| MMVF | Man Made Vitreous Fibers |
| MNDO | Modified Neglect Of Diatomic Overlap |
| MNDO | Modified Neglect Of Differential Overlap |
| MNDO-HE | Modified Neglect Of Diatomic Overlap-half Electron |
| MNDO-PM3 | Modified Neglect Of Diatomic Overlap-parametric Method |
| MNDO/H | MNDO For H-bonded Systems |
| MNDO/M | Modified MNDO |
| MNDOC | Modified Neglect Of Diatomic Overlap Correlated |