The modern definition of a liter is 1 cubic decimeter (a decimeter being 10cm), so 1000 liters = 1 cubic meter.

The official symbol for the liter is the letter L - both upper case L or lower case l are accceptable. This is due to the lower case l looking very similar to the number 1 and the confusiion caused by this caused the upper case L symbol to be introduced.

The current definition was adopted in 1964 and replaced the definition of a liter as 1 kg of pure water at 4 degrees centrigrade and 760 millimeters of mercury pressure, which had made the liter 1.000028 decimeters. (Historically the liter had initially been introduced in France in 1795 as 1 cubic decimeter, only later being redefined in 1901 at the 3rd meeting of the Conference Generale des Poids et Mesures (CGPM) to the 1 kg of pure water at 4 degrees centrigrade and 760 millimeters of mercury.)

The word litre is evolved from an older French unit called the litron, originating from a Greek word.

Liter is the usual spelling of 'litre' in American English and is used only in the United States, other english speaking countries using the litre spelling. French and other European languages use the litre spelling, which originates from the french.