An Etymological Dictionary of Astronomy and Astrophysics

In → plasma physics, → fluid dynamics, and → self-gravitating systems, a particle or ensemble of particles which are affected by the evolution of the rest of the system, but do not affect the rest of the system.
The test particle concept is used, e.g.,
for revealing a flow, describing the path of fluid elements, and so on.

See also: → test; → particle.