Data classification
Sorting data into categories by sensitivity so that protection can be applied proportionately.
Without classification every file is treated the same, which means either over-protecting everything or under-protecting what matters. A workable scheme has three or four levels, not ten.
Classification only becomes useful when it drives something automatic, such as labeling, retention, or a DLP rule. A spreadsheet of categories that changes no behavior is documentation, not a control.
Where this comes up
Data classification sits inside our compliance and frameworks work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.