In many belief systems, spirits are on the same plane of existence as "gods", though of much lesser magnitude. For example, Zeus was a god, and any given dryad was likewise accounted as a spirit in greek mythology.
Many nature religions, such as animism, believe that everything found in nature has a personification, a spirit. These spirits may be prayed to, or in other ways coerced, in order to gain more favourable conditions. In such religions, magic is an integral part of reality, in effect the ability to communicate with the spirits.
Historically, spirits have been ascribed any number of powers, both over nature and over humans. Often a spirit's power is said to be linked with its purpose in creation.
In some parts of the world, spirits are believed to be able to possess humans and control their behaviour.
One could say that Q from star trek are ficshanal spirits as they possess many if not all of the trait mentioned above.