Wiktionary
n. A garden at the rear of a property.
Wikipedia
A back garden is a residential garden located at the rear of a property, on the other side of the house from the front garden. Such gardens have a special place in English suburban and gardening culture.
A back garden arises when the main building divides the surrounding gardens into two. This happens especially in the high density housing of British cities and towns. A semi-detached house typical of the British suburbs of the 20th century will have front gardens which face the road and provide access. The back gardens in such cases will be more secluded and access will typically be via the dwelling or by a path around the side.
If the housing is terraced, then no side path is possible and access may be provided by an alley which runs behind the rear of the terrace. While buildings opening directly onto a street may not have a front garden, most will have some space at the back, however small; the exception being back-to-back houses found in northern industrial towns in England such as Leeds, but now mostly demolished.
A front garden is a formal and semi-public space and so subject to the constraints of convention and law. However, the back garden is more private and casual, and so can be put to more purposes.
Usage examples of "back garden".
We went into the back garden of a big house, and the Lord Mayor courteously explained my purpose to several persons of importance, including Bishop Griffin himself.
The kitchen had a door on to a back garden - stone patio, lawn covered in rotting leaves, an ivy-covered wall giving privacy.
On impulse he stood up and walked to the edge of the lawn, where he pushed aside the high brown grass with the toe of his shoe until he found the first of the brick stepping stones that led out to the back garden.
Next he took two mouthfuls of water and spat them into his back garden.
The grown-up Lamb's voice was so tyrant-like, as Jane said afterwards, that they actually retreated to the back garden, and left him with his little moustache and his flannel suit to meet alone the young lady, who now came up the front garden wheeling a bicycle.