Solipsism is the metaphysical belief that only oneself exists, and that "existence" just means being a part of one's own mental states - all objects, people, etc, that one experiences, are merely parts of one's own mind. One is like a God, creating the reality in which one exists. Solipsism is logically coherent, but not falsifiable, so it cannot be established by current modes of the scientific method.
Solipsism is a common theme in eastern philosophy. Various interpretations of Buddhism, especially Zen, teach that the entire universe exists only in one's mind.
The classic objection to solipsism is that people die. However, you have not died, and therefore you have not disproved it.
A further objection is that life causes pain. Why would we create pain for ourselves? One response to this is that there may be some reason which we have decided to forget, such as the law of Karma, or a desire not to be bored.
A deeper objection, raised by David Deutsch, among others, is that, since you have no control over the "universe" you are creating for yourself, there must be some unconscious part of your mind creating it. If you make your unconscious mind the object of scientific study (e.g. by conducting experiments) you will find that it behaves with the same complexity as the universe offered by realism; therefore, the distinction between realism and solipsism collapses - what realism calls "the universe", solipsism calls "your unconscious mind", but these are just different names for the same thing: both are massively complex processes external to your conscious mind, and the cause of all your experiences.
