The Force was a metaphysical, binding, and ubiquitous power that held great importance for the Jedi and Sith monastic orders.
Described by Jedi Master Obi-Wan Kenobi as "an energy field created by all living things," some societies and organizations thought of the Force as a non-corporeal sentient entity that might be capable of intelligent thought, while others simply considered it something that could be manipulated and used as though it were a tool.
The Force potential of an individual was measured in sentient creatures by a midi-chlorian count. While both the Jedi and the Sith used the Force to gain their power, there were as many different groups of users and views of the Force as uses of the Force itself.
The Force was restored to balance in 4 ABY by the Chosen One, Anakin Skywalker.