From my understanding of the contemporary use of the term, a “Leninist” is someone who believes that the political party is the way for the proletariat to organise itself and exercise its will, the party acts as a vanguard. This is in contrast to some “left communists” who think that the working class can spontaneously organise itself, without the leadership of a vanguard party. But then you have some other left communists, like Bordiga and the ICP who are “Leninists” because they believe the international proletariat should organise itself in a world-encompassing communist party. So Bordiga cannot be considered a “Marxist-Leninist” (socialism in one country, socialism with *-characteristics), but is a “Leninist” (working class should be organised into a communist party).