) is an SI prefix
in the SI
system of units
denoting a factor of 10−24
or 0.000 000 000 000 000 000 000 001.
Adopted in 1991, it comes from the Greek οκτώ, meaning eight, because it is equal to 1/10008. As of 2007, yocto- is the smallest SI prefix to be confirmed.
It can be used for measuring a subatomic particle's mass, for example: