A general stabilizing interaction which involves the delocalization of sigma electrons of a C-H bond of an alkyl group directly attached to an unsaturated system (or) to a species with an unshared p -orbital such as Carbocations (or) free radicals is known as hyperconjugation. Hyperconjugation is a permanent effect. Ex: Hyperconjugation in ethyl carbo cation. One of the carbon-hydrogen bonds of the methyl group aligns in the same plane with the empty p -orbital of the positively charged carbon atom.
In simple words the movement of sigma bond is called hyperconjugation….OrFormation of pie bond due to breaking of sigma bond by side by side overlapping is called hyperconjugation