Two-dimensional region of a sample surface at the analytical point, but set in the plane at right angles to the spectrometer axis, from which the entire analytical signal or a specified fraction of that signal is detected.
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1797 (https://doi.org/10.1515/pac-2019-0404)