Some liquids on mixing form 'azeotropes'. What are 'azeotropes'?

Azeotropes are mixtures of two liquids which boil at a constant temperature and can be distilled unchanged in their composition. These are formed by non ideal solutions. Examples of azeotropes include HNO3+H2O, HCl+H2O, C2H5OH+CCl4, CHCl3+CH3COOCH3