A set of tendencies of different origins that identify with and give priority to what the Second International called the "maximum program": the abolition of the state and wage labor.
Origin of maximalism
During the 19th century both Marxists and collectivist anarchists were usually described as maximalists... and not only by the reformist tendencies.
In Russia, the revolutionary faction of the Socialist Revolutionaries, the party of the peasant revolution, would call itself socialist-maximalist and would end up merging with the Bolsheviks, the Inter-District Organization (Mezhraiontsy) and other groups in the process of formation of the Communist Party of Russia (Bolshevik) in 1917.
Unaware of the divisions within Russian socialism, the Belgian, French, Spanish, Portuguese and Italian press, including the socialist press, routinely identified the Bolsheviks as maximalists throughout the Russian revolutionary process and the first years after the revolution. The headline with which El Socialista, the official daily of the Spanish Socialist Workers' Party, reported the October insurrection was none other than: The Triumph of the Maximalists.
The identification between the term maximalist and the Russian revolution was such in the early period of the Third International that its first organization in Portugal, the first Portuguese communist party, founded in 1919, was officially called Federação Maximalista Portuguesa (FMP).
Something similar happened in Italy, where Bordiga and Gramsci referred to the Bolsheviks as maximalists at least until 1920. The pro-Third International current then emerging in the Italian Socialist Party began to be called, and to recognize itself, as maximalist. That is why the abstentionist fraction within this current -led by Bordiga and the origin of the later Italian communist left- declared its maximalist orientation and regularly spoke of the maximalist proletariat and of maximalist socialism.
In Italy, however, the name went down in history associated with the centrist electoralist fraction headed by Serrati. Partly because in 1921 the left maximalists led the founding of the Italian Communist Party, and partly because Lenin would criticize Serrati and his followers as the electoral maximalists, and the following generations, who no longer kept in mind that both right and left were known as maximalists at the time, began to abbreviate and call the centrist current and Serrati simply maximalists.
From 1924 onwards the term ceased to be used by communists to refer to themselves and its use became increasingly restricted. Generally, and always in the mouths of others, it designates sectoral movements more or less organized by the International.
It appears, for example, in references to the communist co-operators and other fractions promoted by the United Front policy. In Spain it would reappear in the 1930s, used by the parties of the republican petty bourgeoisie to refer to a confused array that would include insurrectionist elements of anarcho-syndicalism and the Spanish communist left, and in 1937 to the forces that took part in the revolutionary movement, defending it from the attacks of Stalinism and the republican government (basically, the CNT rank and file, the Friends of Durruti and the Spanish Bolshevik-Leninist Group). After 1937 the term dropped out of political language and was used less and less.