WHAT SNUBBER DIODE DO IN FLYBACK AND SWITCH POWER

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This is "horizontal flyback" when talking about CRT screens: - 

This is unrelated to the term "flyback transformer" other than the fact that the "method" and the "device" are both "used" inside an old TV or oscilloscope.

The term "flyback pulse" probably refers to the well-known problem that flyback SMPS's have when switching - not all the energy taken-in by the primary can be released to the secondary and this creates a back-emf that needs to be snubbed out else the output transistor may fail. It usually looks like a pulse and is controlled (limited) on the primary side of the transformer by Rs, Cs and Ds shown below.

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