A Laser oscillator in which two mirrors are separated by an amplifying medium with an inverted population, making a Fabry-Perot cavity. Standard Diode lasers are Fabry-Perot lasers.

A Fabry-Perot cavity is the standard cavity with two highly reflecting mirrors bouncing the Light back and forth, forming a standing wave. This cavity is not very Frequency selective, theoretically you could have 1 mm Wavelength light and .001 Micron wavelength light in the SAME cavity, as long as the mirrors are the right distance apart to form a standing wave.

Fabry-Perot lasers are made with a Gain region and a pair of mirrors on the facets, but the only wavelength selectivity is from the Wavelength Dependence of the gain and the requirement for an integral number of wavelengths in a cavity round trip.

A Fabry-Perot by definition consists of two planar mirrors, but the term is nowadays very frequently also used for resonators with curved mirrors. From a theoretical viewpoint, plane-plane Optical Resonators are special in the sense that their Resonator Modes extend up to the edges of the mirrors and experience some Diffraction losses. However, Fabry-Perots are usually used with input beams of much smaller diameter, which are actually not really matched to the resonator modes. For the usually small mirror spacings, where diffraction within a round trip is rather weak, this deviation does not matter that much.