in simple terms, dictatorship of the proletariat means that the proletariat (the working class, those of us who make our income by selling our labor power) controls the state apparatus as a class
as opposed to the dictatorship of the bourgeoisie, which means the bourgeoisie (the capitalist class, those who make their income by owning the means of production) controls the state apparatus as a class
the second is the current state of things in most countries around the globe