From AMS Glossary
Any of the many types of objects detected by radar.
A radar target must have an index of refraction sufficiently different from that of the atmosphere to return a target signal to the radar by reflection, refraction, or scattering. Also, it must be near enough and have a large enough radar cross section that the target signal will exceed the threshold of detectability of the radar receiver. The target is then said to produce a detectable echo.