Socialism, in its many philosophical and social scientific manifestations, is grounded in the idea that the best of all possible human societies is one based on cooperation and nurturing, rather than competition and greed.  As a guiding philosophy for organizing family life, socialism has widespread support, even among conservatives.  Nevertheless, socialism is a protean concept:  defined, for social scientific purposes, in many different ways --- presenting different faces, as it were.  It is defined within Marxian theory as a transitional stage between capitalism and communism:  a stage within which the capitalist economy is controlled by a pro-worker government that gradually puts into place the conditions for communism. Some have further defined socialism as implying a change in property ownership, such that the major capitalist enterprises become state capitalist enterprises (owned by the state and used for the purpose of bringing about the aforementioned transition).  Socialism can also be defined, in a non-Marxian manner, as simply implying a pro-worker government that will use state policies to improve the lives of working people without any presumption that the state will try to create communism.  Indeed, some socialists (defining their socialism in this non-Marxian way) might even be opposed to communism and simply favor a more benign form of capitalism (the Swedish "Middle Way," perhaps).
Socialism became popular in the 19th century.  It is during this period that the protean nature of the concept was produced by a wide range of social theorists, including Marx.  These theorists did not always agree about the nature or goals of socialism, but generally shared a concern for working people and others who were marginalized in the growing capitalist economy and society and a belief that capitalism was, by the nature of how it came into being and the mechanisms that reproduced it, unjust.  Socialist parties are relatively common in most nations.  The French Socialist Party is one of the most important political institutions in that nation.  The British Labor Party was, for a long time, a socialist party, although it has abandoned that rhetoric of late.

"May there not be found a mode of labour consistent with
security which will not only obviate the evils of individual competition, but which will afford its peculiar benefits--- abundant production and development of all the faculties--- to a greater, an incalculably greater extent, than the best arrangements of individual competition could afford."

---William Thompson (1850)