Environmental Studies
- Mass Movement
- mass provisioning
- Mass wasting
- mass-wasting
- mating system
- mating type
- mature phase
- meadow steppe
- mechanical weathering
- median network
- median valley
- Medical Waste
- mediolittoral
- Mediterranean climate
- Mediterranean floral region
- Mediterranean forest
- Mediterranean scrub
- megathermal climate
- meiofauna
- mesa (geology)