pre. In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 10−24. Symbol: y
Yocto- (symbol y) is a unit prefix in the metric system denoting a factor of 10 or .
It was adopted in 1991 by the General Conference on Weights and Measures. It comes from the Latin/Greek , meaning "eight", because it is equal to 1000. Yocto- is the smallest official SI prefix.