An imaginary plan of social reorganization, outside the dynamics and social forces actually present, which is proposed as a universal solution if imposed on reality.
The defining character of utopias is not so much to be placed in an imaginary place as to do so outside historical time, that is, outside the real movement of society. Utopia is a plan to be implemented, a scheme to be imposed on reality. That is why, from the first appearances of the proletariat as a political class, utopias are necessarily reactionary: they express more the desire to place themselves on the margin of the class struggle, than the communist objective that with a more or less deep foundation- many of them proclaim.
That is also why class consciousness is “anti-utopian” and “The Manifesto” already emphasizes this when it characterizes the communists.
[The communists] do not proclaim special principles to those who would like to shape the proletarian movement, […] theoretically, they have the advantage over the rest of the proletariat of their clear vision of the conditions of the march and the general results of the proletarian movement.
“Manifesto of the Communist Party”, 1848