A "dim object" refers to something that is not very bright or not easily seen in the dark. It can also be used metaphorically to describe something that lacks brilliance or is not very significant. Full definition
These very dim objects may be more representative of the early universe, and offer new insight on the formation and evolution of the first galaxies. (sciencedaily.com)
Long exposures are required to capture as much light as possible from potentially dim objects. (sciencedaily.com)
A larger lens or mirror allows you to see dimmer objects and to resolve finer detail. (discovermagazine.com)