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Coherent light is light consisting of coherent waves, i.e., matching in wavelength. The term is generally used for waves from a point source or for plane waves (basically, a beam of waves moving in the same direction, the waves in lock-step). In concept, coherent light could be from separated sources if the separate light beams have the same similarity (e.g., identical to that from a point source masked to produce separate beams). Lasers (the visible light analog of masers) produce a beam of such light, all the light the same wavelength, which is unchanging, and very nearly in plane waves, i.e., the beam is moving very close to parallel.
One 1995 astronomical observation has been interpreted as what could be called a natural laser, but word maser is often used in astronomy for any such coherent EMR source, and masers of other EMR (such as microwaves) are common. Lasers (the artificial kind) are also used for adaptive optics, and in gravitational-wave detectors.