The yard (abbreviation: yd) is an English unit of length, in both the British imperial and US customary systems of measurement, that comprises 3 feet or 36 inches. It is by international agreement in 1959 standardized as exactly 0.9144 meters. A metal yardstick originally formed the physical standard from which all other units of length were officially derived in both English systems.
In the 19th and 20th centuries, increasingly powerful microscopes and scientific measurement detected variation in these prototype yards which became significant as technology improved. In 1959, the United States, United Kingdom, Australia, New Zealand, and South Africa agreed to adopt the Canadian compromise value of 0.9144 meters per yard.
