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A cataclysmic variable star (CV or cataclysmic variable) is a variable star that irregularly grows in magnitude by a large factor, the extra brightness lasting for some time and subsiding. These events of temporary brightening are termed novae. The mechanism creating these events is a white dwarf accreting matter from a binary companion to the point that fusion is ignited, but is sustained only temporarily.
The terms cataclysmic variable (and to some degree, nova) are also used in a more general sense, for any star that becomes distinctly brighter on occasion, i.e., as a classification based upon appearance. In this case, the above-described white-dwarf scenario is merely a common underlying mechanism.