Democratic centralism is a way of organising a political party or political movement. It was originated by Vladimir Lenin, leader of the Russian Social Democratic Labour Party (later, Communist Party) in the context of high working-class rebelliousness and potentially immanent revolution, but also tight state repression, that characterised Russia just before the 1917 Communist revolution. His intent was to maintain democratic control of the Party by its members, whilst establishing a clear hierarchy and chain of command which would enable the Party to manuever with the decisiveness, secrecy, and speed, that the situation demanded.
Democratic centralism remains the organising principle of many (all?) of the Communist Parties formerly associated in the Third Communist International.
The key principle of democratic centralism is `democracy in discussion, unity in action': all party members are free to express any opinion and vote as they please during the decision-making assemblies of the party, but once a decision is reached they must not dissent publicly from it, and are bound to act according to the majority decision.
It is important that the democratic aspect and the centralism aspect be kept in balance; and that balance should shift according to circumstances. In more liberal, but also less revolutionary times, the party can afford, but also needs to be more demacratic and open; whereas in a tough revolutionary battle the party needs to be tight. As the marxists.org glossary article says:
Too much democracy in action leads to disorganisation and confusion, and usually defeat; too much centralism in discussion leads to bureaucratism, bad decisions and a loss of commitment among members.
`Democratic Centralism', Marxists.org Glossary of Terms.
[ http://marxists.org/glossary/terms/d/e.htm ]