Also known as ‘cambric’, chambray is a plain woven, medium weight cotton fabric. Usually made from blue and white yarns, it’s used to make shirts, dresses and children’s clothing. It takes its name from the town of Cambrai in the north of France.
A heavier version was used for workmen’s shirts in the USA and as such supposedly the source for the term ‘blue collar’.
Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary