A quart is a unit of measurement for volume. It is equal to two pints. There are several different units known as a pint, and so there are accordingly several different quarts.

• US liquid measure:
  • equal to two US liquid pints
  • equal to four US liquid cups
  • defined as one quarter of a US gallon
  • equal to 32 US fluid ounces
  • equal to 0.946352 litres

• US dry measure ("dry quart"):
  • equal to two US dry pints
  • defined as 1/32 of a US bushel
  • equal to 67.2 cubic inches
  • equal to 1.101220 litres

In imperial (UK & Canadian) measure a quart is a measure of capacity, liquid or dry

• Imperial measure:
  • equal to two imperial pints
  • defined as one quarter of an imperial gallon
  • equal to 40 imperial fluid ounces
  • equal to 1.1365225 litre exactly

The UK legal definition of the (imperial) quart is 1.1365225 litres precisely in The Units of Measurement Regulations 1995
http://www.hmso.gov.uk/si/si1995/Uksi_19951804_en_2.htm

Reference

Guide for the Use of the International System of Units (SI) US government publication; includes US-(liquid)-to-litre & imperial-to-litre conversion

Quart is also a municipality in Gironès comarca, Girona province, Catalonia, Spain.