"Reality and unreality collide on such a fundamental level that each becomes the other and anything is possible, within certain parameters."(Douglas Adams, LU&E)
An alternative path or perception, another view of things, UN-real to the person who has determined something else as REAL.
Perhaps reality is best defined as a knowingly or unknowingly chosen view of the universe and its laws and behaviors. Subject to change and reinterpretation as one cracks his shins upon the things others agreed on that he has ignored...