What is "disproportionation"

n. 1 (context chemistry English) A form of redox reaction in which part of a reactant is oxidized and part of it is reduced simultaneously 2 (context chemistry English) A reaction wherein a single reactant generates two chemical species which are different from each other and the initial reactant.

Disproportionation is a specific type of redox reaction in which a specie is simultaneously reduced and oxidised to form two different products.