You and I are spirits existing in a human body. A traditional ghost is a spirit that was once in a human body. If your beliefs tend to lean towards animism, all living beings and objects contain a spirit, not just ghosts of people that are now departed. A spirit is consciousness that resides in a physical or etheric body.
There are many types of spirits and beings existing in this world; some dwell in houses, some in rivers, in trees, in rocks, and even within the land itself.
Land spirits are the collective consciousness that exist in an area; some might be a valley, or a hill, or a place where massive apartment complexes now sit. Land spirits exist in densely populated areas, and not just in forests and wild areas.
A familiar is not a pet. Pets can be beloved, amazing companions and family members, however, they are rarely familiars. A familiar is a being that works with a witch or sorcerer and assists them with either performing magical tasks, or protecting them. A familiar may or may not have a physical body.
Nature beings are often referred to as faeries, but this term when used in the United States frequently is an umbrella term for quite a broad spectrum of beings, each with their own culture, rules, and way of existing in the world. Not all of these beings are safe for people to work with, nor do all of them value human life or have an interest in communicating with people. (They are not ultra thin, hyper sexualized, traditionally beautiful white women with wings, just to be clear)