Label Preferences - Measurement Suffix
The Measurement Suffix defines the defaults used when inserting labels.
Area, Length and Number (Each) labels will use the values in preferences respectively as their Measurement Suffix. Like all default settings, these can be changed subsequently by the various Edit Labels tools.
The measurement type can be expressed within the label's text by using the %measurementtype% macro. For a full list of the macros that can be used see the Label Template Reference page.