Definition from Wiktionary, the free dictionary
backyard (plural backyards)
- A yard to the rear of a house or similar residence.
- (colloquial) A person's neighborhood, or an area nearby to a person's usual residence or place of work and where the person is likely to go.
- (colloquial) An area nearby to a country or other jurisidiction's legal boundaries, particularly an area in which the country feels it has an interest.
1942, Wilfrid Hardy Callcott, The Caribbean policy of the United States, 1890-1920, page 343:
- However, the region was in the United States backyard and Britain should look passively on with acquiescence in whatever policy the United States saw fit to pursue about Mexico.
Note that backyard is usually written as a single word, while front yard is always written as two words.
yard to the rear of a house