Manual focus. The photographer adjusts the lens to obtain the image sharpness required, as opposed to AF. Alternative meaning: Medium Format. A size of film or image sensor somewhat larger than the 35mm film standard of 36 × 24 mm. Found on http://en.wikipedia.org/wiki/List_of_abbreviations_in_photography
abbreviation: Mandatory Frequency (Canada uncontrolled aerodromes/airports), also, Medium Frequency (1600 to 3000 kHz -traditional radio communications useage or 300-3000kHz current DOD useage)
Found on http://www.encyclo.co.uk/local/20021