The noun yard has two main meanings.
A yard is a unit of length in the imperial system of measurement. It is equal to thirty-six inches, or approximately 91.4 centimetres.
Jack was standing about ten yards away.
In Britain it is becoming more common to give measurements in metres, rather than yards.
area around a house
In both British and American English, a yard is an area of ground attached to a house. In British English, it is a small area behind a house, with a hard surface and usually a wall round it. In American English, it is an area on any side of a house, usually with grass growing on it. In British English, a fairly large area like this is called a garden or back garden.