Look up tera in Wiktionary, the free dictionary. 
Tera is a unit prefix in the metric system denoting multiplication by one trillion, or 10^{12} or 1000000000000 (one trillion short scale; one billion long scale). It has the symbol T. Tera is derived from the Greek word τέρας teras, meaning "monster"; also it resembles tetra, meaning "four" but with the middle letter removed as it is the fourth power of 1000.^{[1]} The unit prefix was confirmed for use in the International System of Units (SI) in 1960.
Examples of its use:
 terahertz radiation: electromagnetic waves within the band of frequencies from 0.3 to 3 THz. Visible light is around 500 THz.
 terabit and terabyte, units used in data storage. Tebi, or 2^{40} is the closest binary prefix being ≈9.95% greater than 10^{12}.
 teragram: equal to 10^{9} kg. The Great Pyramid of Giza has a mass of about 6 Tg.
 terasecond: approximately 31,558 years
 teralitre: equal to 10^{9} m^{3}. Lake Zurich contains about 4 TL of water.
 terawatt: used to measure total human energy consumption. In 2010 it was 16 TW (TJ/s).
 terametre (= 1,000,000,000 km): Light travels 1.079 Tm in one hour.
Prefix  Base 10  Decimal  English word  Adoption^{[nb 1]}  

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

See also
References
 ^ C. Upward, G. Davidson, The History of English Spelling, WileyBlackwell (2011)