Final answer:
The units of measurement in the distance field for the output feature class, when a GIS analyst performs a distance join and the data frame uses a projected coordinate system with meters, will be in meters.
Step-by-step explanation:
When a GIS analyst is performing a distance join between two feature classes where the feature classes use a geographic coordinate system but the data frame uses a projected coordinate system with meters as the unit of measurement, the units of measurement in the distance field for the output feature class will be in meters. This is because the actual calculations for distance are performed based on the coordinate system of the data frame, not the feature classes themselves. If the data frame is set to a projected coordinate system that uses meters, then the output will reflect this unit of measurement.
Understanding that different coordinate systems have different units of measurement is important. A geographic coordinate system typically measures in degrees since it reflects the curvature of the Earth. In contrast, a projected coordinate system converts the curved surface of the Earth to a flat plane and measures distance in linear units such as meters, feet, or kilometers. Since the data frame's projected coordinate system is set to use meters, all the distances calculated will be in meters, even though the feature classes are in a geographic coordinate system.