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M
Manual iris.  A lens with a manual method of varying the size of the aperture.
Matrix.  A mathematical array.  A logical network configured in a rectangular array of
intersections of input/output channels.
Matrix switcher.  A device for switching more than one camera, VCR, video printer and
similar, to more than one monitor, VCR, video printer and similar.  Much more complex
and more powerful than simple video switchers.
MATV.  Master Antenna TeleVision.
MB.  Megabyte.  Unit of measurement for computer memory consisting of approximately one
million bytes.  Actual value is 1,048,576 bytes.  Kilobyte × Kilobyte = Megabyte.
MB/s.  Megabytes per second.  Million bytes per second or 8 million bits per second.  Also
written as MBps.
Mb/s.  Megabits per second.  Million bits per second. Also written as Mbps.
MHz.  Megahertz.  One million hertz.
Microwave.  One definition refers to the portion of the electromagnetic spectrum that ranges
between 300 MHz and 3000 GHz.  The other definition is when referring to the transmission
media where microwave links are used.  Frequencies in microwave transmission are usually
between 4 GHz and 60 GHz.
MOD.  Minimum Object Distance.  Feature of a fixed or a zoom lens that indicates the closest
distance an object can be from the lens's image plane, expressed in meters.  Zoom lenses have
MOD of around 1 m, while fixed lenses usually much less, depending on the focal length.
Modem.  This popular term is made up of two words: MOdulator and DEModulator.  The
function of a modem is to connect a device (usually computer) via an audio (usually) telephone
line to another device with a modem.  It converts the digital computer signal to audio tones.
Modulation.  The process by which some characteristic (i.e., amplitude, phase) of one wave
(carrier wave) is varied in accordance with another wave (modulating or message signal).
Moiré pattern.  An unwanted effect that appears in the video picture when a high-frequency
(lines close together) pattern is looked at with a CCD camera that has a pixel pattern close to
(but lower) the object pattern.
Monochrome.  Black-and-white video.  A video signal that represents the brightness values
(luminance) in the picture, but not the colour values (chrominance).
MPEG.  Motion Picture Experts Group.  An ISO group of experts that has recommended
manipulation of digital motion images.  Today there are a couple of MPEG recommendations,
of which the most well known are MPEG-1 and MPEG-2.  The latter one is widely accepted
for high definition digital television, as well as multimedia presentation.
MPEG-1.  Standard for compressing progressive scanned images with audio.  Bit rate is from
1.5 Mbps up to 3.5 Mbps.
MPEG-2.  The standard for compression of progressive scanned and interlaced video signals
with high quality audio over a large range of compression rates with a range of bit rates from
1.5 to 100 Mbps.  Accepted as a HDTV and DVD standard of video/audio encoding.
Multiplexing.  In CCTV it is correctly named Time Division Multiplexing and is the technique
used to enable a number of video inputs (up to 34) to be recorded onto a single tape.  Frequency
Division Multiplexing is a technique used to allocate individual frequencies within a band of
frequencies.  In fibre Optic systems there is also Wavelength Division Multiplexing WDM, and
Dense Wavelength Division Multiplexing DWDM where a number of wavelengths of light can
share the same fibre, to enable more information to be communicated.
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