"Nit (unit)" redirects here. For the unit of information entropy, see Nat (information).
The candela per square metre (cd/m²) is the SIunit of luminance; nit is a non-SI name also used for this unit. It is often used to quote the brightness of computer displays, which typically have luminances of 50 to 300 nits (the sRGB spec for monitors targets 80 nits). Modern flat-panel (LCD and plasma) displays often exceed 300 cd/m² or 300 nits.
"Nit" is believed to come from the Latin "nitere" = to shine.
References
IEC 61966-2-1:1999 is the official specification of sRGB.