Non-negative parameter characterizing the dispersion of the quantity values that are being attributed to a measure based on the information used.
Where possible, this should be derived from an experimental evaluation but can also be an estimate based on other information, e.g. experience.
Definition from CEOS-WGISS Glossary of Acronyms and Terms, v1.0

https://earthdata.nasa.gov/user-resources/glossary#visualization