A yobibyte is a unit of data storage that equals 2 to the 80th power, or 1,208,925,819,614,629,174,706,176 bytes.
While a yottabyte can be estimated as 10^24 or 1,000,000,000,000,000,000,000,000 bytes, a yobibyte is exactly 1,208,925,819,614,629,174,706,176 bytes. This is to avoid the ambiguity associated with the size of yottabytes. A yobibyte is 1,024 zebibytes and is the largest unit of measurement.
For a list of other units of measurements, view this Help Center article.