Algol (Beta Persei, β Persei, Beta Per, or β Per) is a triple star system including an Eclipsing Binary, and whose stars do not appear to match normal Main-Sequence evolution, a consequence of mass transfer between stars.
Characteristics (β Per Aa1):
The "wrong" characteristics of the stars due to the Accretion between stars is known as the Algol Paradox. It is also the prototype for a class of Variable Stars called Algol Variables, or just Algols.
Post-common Envelope Binary (PCEB)