I've understood it as meaning a policy of allowing industrialization to build and the implementation of the dictatorship of the proletariat in a country after a revolution. It specifically seems to refer to Stalin's plan of industrialization of the Soviet Union, taking a relatively undeveloped country and making it stand up against the industrialized giants of the West at that time. Trots and left comms like to say this makes us "nationalists", which is just bullshit. We Marxist-Leninists are still vehemently internationalist and the build up of socialism in a country should be done alongside supporting revolutions across the globe.