What is Resolution?

Broadly speaking, resolution is the ability to detect differences in measured units. For spectroscopy experiments, the measured unit is the quantity used to describe the photon (e.g. wavelength, wavenumbers, frequency, energy). For example, if the resolution of an experiment is 1 nm, then the experiment can tell the difference between peaks at 500 nm and 501 nm, but it cannot tell the difference between peaks at 500 nm and 500.5 nm. The observed resolution in an experiment depends on the linewidth of the transition and the spectral resolution. In most instances, only one contribution to the experiment is significant and the other can be ignored.