Mega
Mega is a unit prefix in metric systems of units denoting a factor of one million (10^{6} or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from Ancient Greek: μέγας, romanized: megas, lit. 'great'.[1]
Look up mega in Wiktionary, the free dictionary. 
Common examples of usage
 Megapixel: 1 million pixels in a digital camera
 One megatonne of TNT equivalent amounts to approx. 4 petajoules and is the approximate energy released on igniting one million tonnes of TNT. The unit is often used in measuring the explosive power of nuclear weapons.
 Megahertz: frequency of electromagnetic radiation for radio and television broadcasting, GSM, etc. 1 MHz = 1,000,000 Hz.
 Megabyte: unit of information equal to one million bytes (SI standard).
 Megawatt: equal to one million watts of power. It is commonly used to measure the output of power plants, as well as the power consumption of electric locomotives, data centers, and other entities that heavily consume electricity.
 Megadeath: (or megacorpse) is one million human deaths, usually caused by a nuclear explosion. The term was used by scientists and thinkers who strategized likely outcomes of allout nuclear warfare.
Exponentiation
When units occur in exponentiation, such as in square and cubic forms, any multiplesprefix is considered part of the unit, and thus included in the exponentiation.
 1 Mm^{2} means one square megametre or the size of a square of 1000000m by 1000000m or 10^{12}m^{2}, and not 1000000square metres (10^{6} m^{2}).
 1 Mm^{3} means one cubic megametre or the size of a cube of 1000000m by 1000000m by 1000000m or 10^{18} m^{3}, and not 1000000cubic metres (10^{6} m^{3})
Computing
In some fields of computing, mega may sometimes denote 1,048,576 (2^{20}) of information units, for example, a megabyte, a megaword, but denotes 1000000 (10^{6}) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. The prefix mebi has been suggested as a prefix for 2^{20} to avoid ambiguity.
Prefix  Base 1000  Base 10  Decimal  English word  Adoption[nb 1]  

Name  Symbol  Short scale  Long scale  
yotta  Y  1000^{8}  10^{24}  1000000000000000000000000  septillion  quadrillion  1991 
zetta  Z  1000^{7}  10^{21}  1000000000000000000000  sextillion  trilliard  1991 
exa  E  1000^{6}  10^{18}  1000000000000000000  quintillion  trillion  1975 
peta  P  1000^{5}  10^{15}  1000000000000000  quadrillion  billiard  1975 
tera  T  1000^{4}  10^{12}  1000000000000  trillion  billion  1960 
giga  G  1000^{3}  10^{9}  1000000000  billion  milliard  1960 
mega  M  1000^{2}  10^{6}  1000000  million  1873  
kilo  k  1000^{1}  10^{3}  1000  thousand  1795  
hecto  h  1000^{2/3}  10^{2}  100  hundred  1795  
deca  da  1000^{1/3}  10^{1}  10  ten  1795  
1000^{0}  10^{0}  1  one  –  
deci  d  1000^{−1/3}  10^{−1}  0.1  tenth  1795  
centi  c  1000^{−2/3}  10^{−2}  0.01  hundredth  1795  
milli  m  1000^{−1}  10^{−3}  0.001  thousandth  1795  
micro  μ  1000^{−2}  10^{−6}  0.000001  millionth  1873  
nano  n  1000^{−3}  10^{−9}  0.000000001  billionth  milliardth  1960 
pico  p  1000^{−4}  10^{−12}  0.000000000001  trillionth  billionth  1960 
femto  f  1000^{−5}  10^{−15}  0.000000000000001  quadrillionth  billiardth  1964 
atto  a  1000^{−6}  10^{−18}  0.000000000000000001  quintillionth  trillionth  1964 
zepto  z  1000^{−7}  10^{−21}  0.000000000000000000001  sextillionth  trilliardth  1991 
yocto  y  1000^{−8}  10^{−24}  0.000000000000000000000001  septillionth  quadrillionth  1991 

See also
References
 "Oxford English Dictionary (OED Online)". www.oed.com (3rd ed.). Oxford University Press. June 2001. Retrieved 20170918.
Origin: A borrowing from Greek. Etymon: Greek μεγα. ... Forming scientific and technical terms with the sense ‘very large’, ‘comparatively large’, or (esp. in Pathol.) ‘abnormally large’, often having correlatives beginning micro, and sometimes also synonyms beginning macro.