a metric unit of capacity, formerly defined as the volume of one kilogram of pure water under standard conditions; now equal to 1,000 cubic centimeters (or approximately 1.75 pints)
"The recipe called for two liters of milk, which is roughly four cups in imperial measure."
Alternative form of litre, one cubic decimeter.
"The metric system defines a liter as an alternative spelling for litre, which is equivalent to one cubic decimeter."
In plain English: A liter is a standard unit used to measure volume, roughly equal to how much liquid fits inside a large juice carton or soda bottle.
"The recipe calls for two liters of water to make the soup."