Meditation is a practice or process of controlling and removing the fluctuations of the mind that manifest as thoughts. This process is used to relax the body and calm the mind. The purpose of meditation is to reach a state of extreme relaxation and concentration. The ideal state is when the body is at rest and the mind is quieted of idle chatter or thoughts.
The idea behind meditating is to reach a higher spiritual level and to engage the mind in higher thinking practices. The way we do this is by quieting the mind, which is exactly what meditation aims to do.
Though most meditation practices come from religious origins, you do not need to be religious to experience the benefits of meditation. As a matter of fact, meditation itself need not be religious or spiritual at all.