This is something that has been forgotten by many.
According to Marxism-Leninism, a capitalist society is one in which
1) the means of production — factories, land, etc., — are owned by individuals or corporate groups of individuals called capitalists;
2) this class of capitalists holds political power by controlling the state apparatus;
3) production is regulated by the profit motive; and
4) exploitation occurs, in that capitalists live, partly or wholly, on the labour of others, i.e., of their employed workers.
On the other hand, according to Marxism-Leninism a socialist society is one in which
1) the means of production are owned collectively by the workers;
2) this class of workers holds political power by controlling the state apparatus;
3) production is planned by the state; and
4) exploitation — the process of living partly or wholly on the labour of others — has been eliminated.
On the basis of these definitions, Marxist-Leninists describe the society which was constructed in the Soviet Union in the period following the revolution as a socialist society.