Spatial resolutionSpatial resolution is the ability of a detection system to record details of the objects under study. In imaging it is usually defined in terms of how close two features can be within an image and still be recorded as distinct. A frequently used resolution limit is given by the Rayleigh Criterion, which applies in ideal conditions but can be much worse in practice. In many practical situations, the Half Intensity Width of the Point Spread Function is a good definition of resolution (it can be calculated for all directions of space, interesting in a 3D microscope).
Other limits similar to Rayleigh's are established by the Abbe criterion, the Dawe criterion and the Sparrow Criterion.