Just as we can speak of the physical plane and the physical world, so can we speak of the astral plane and the astral world. A "plane" (like a "level") is descriptive of the characteristics of the things that make up a world—the substance, energies, laws, etc. A "world," in contrast, is descriptive of how the things are put together, hence the landscape, the life-forms, the climates, and so forth.
The astral world has its own landscape, generally replicating the physical world, but is far more extensive, reaching wherever consciousness reaches. It has its own inhabitants, which include the astral bodies of the inhabitants of the physical world. Those astral inhabitants also include forms that have never incarnated into physical bodies as well as temporary inhabitants created by humans through the power of imagination, emotion and fantasy.
It is also possible that some creatures, like certain paranormal entities such as UFOs, Aliens, the Loch Ness and other "monsters" that slip in and out of the physical world have their origin in the astral, and that mythical beings like dragons also exist in the lower astral close enough to the physical that they sometimes appear to the physical world inhabitants.