What is a star like body in space a small planet?

A star-like body in space that is smaller than a typical planet could refer to a brown dwarf. Brown dwarfs are substellar objects that are too massive to be considered planets but not massive enough to sustain hydrogen fusion like true stars. They typically have masses between those of the largest planets and the smallest stars, forming in a similar way to stars but failing to ignite. These objects can emit faint light and heat from gravitational contraction rather than from nuclear fusion.