Well-known solar activity cycle is far to be just a cyclic behavior of sunspot numbers. An activity wave propagates in earth solar hemisphere from middle latitudes to the solar equator. A more or less standard explanation of the phenomenon is given in terms of so-called dynamo based on joint action of differential rotation and mirror-asymmetric convection (or turbulence). From the formal viewpoint the problem can be presented as a system of coupled parabolic equation rather to a wave equation. This formal distinction with conventional theory of wave propagation results in various peculiar feature of solar (and stellar) activity waves. For a long time activity waves was known for the Sun only while recently stellar activity observations become sufficient to isolate this phenomenon in stellar activity data. We discuss general properties of stellar activity waves in context of recent observational data.

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