The Force is an impersonal energy field that connects all things according to Jedi philosophy. At its most basic, there are two sides of the Force, the Light and the Dark. Some feel it is more correct to say that one's approach to the Force is either Light or Dark, as the Force is, in fact, impersonal.
The Source Material:
The Star Wars movies paints the Light and Dark sides as fairly clear-cut. Those who used the Light side defended others, preserved life, were selfless, calm and rational and approached all matters with detachment. They were the good guys. Those who used the Dark side were selfish, angry, self-absorbed, and destructive. They were the bad guys.
Real Life Beliefs Following the Movies:
Many real-world Jedi understand the Force in terms comparable to ideas in the movies. The Jedi Code, for example, stresses peace and knowledge while eschewing emotion and ignorance, while the Jedi Creed stressed the role of Jedi as protectors of peace and life. The Light side is good and to be embraced while the Dark side is an evil temptation to be avoided.
Finding Balance in the Force:
Some Jedi, however, find the dichotomy between Light and Dark to be unnatural or at the very least an embrace of extremism. They seek to find a harmonious middle ground. Some adopt terms such as following the Shadow side. These Jedi accept that life cannot always be orderly and pacifistic and that emotion can be put to positive end, but likewise understand that falling prey to the extremes of the Dark side are still very much undesirable.
