A source with an angular size less than the resolution of the instrument used to observe it, and therefore unresolved. Stars appear as point sources to the human eye. An object that appears as a point source at some wavelengths (e.g. long radio wavelengths) may be resolvable at shorter wavelengths, or with other instruments. See alsoextended source.
Geology and Earth Sciences
A source of energy which is considered to originate from a point and to have no effective size in relation to its observed effects, e.g. an explosive shot, a current electrode in electrical resistivity sounding, etc.