The term universe has a variety of meanings based on the context in which it is described. In materialist philosophical terms, the universe is the summation of all matter that exists and the space in which all events occur which has an equivalent idea amongst some theoretical scientists known as the total universe. In cosmological terms, the universe is thought to be a finite or infinite space-time continuum in which all matter and energy exist. (It has been hypothesized by some scientists that the universe may be part of a system of many other universes, known as the multiverse.) The terms known universe, observable universe, or visible universe are often used to describe the part of the universe that can be seen or otherwise observed by humanity. Due to the fact that cosmic inflation removes vast parts of the total universe from our observable horizon, most cosmologists currently accept that it is impossible to observe the whole continuum and may use our universe, referring only to that knowable by human beings in particular.