The definition of “Socialism” depends upon whether they are trying to convince you you are wrong to describe someone as a Socialist, or whether they’re trying to persuade you of the glorious wonders and diversity of Socialism. Under the first definition, Socialism is defined narrowly, in it’s putative original sense as the State ownership of the means of production. Under the later, “no, you just don’t understand, there is a wide variety of Socialisms, including market Socialism, and the Socialism espoused by European Social-democratic parties,” or the Socialism of the Newsweek cover “We’re All Socialists Now,” the Socialism of Norman Thomas, of the Fabians, and of Alynskists. These didn’t boil down to instant nationalization and de jure ownership of the means of production: after all, why be saddled with the full responsibility, when you can control them through bureaucratic directive, and retain the de jure owners for management of the details and as scapegoats when things go wrong? The wily Socialist soon realized it was possible to separate power from responsibility, and that to control a thing didn’t mean they had to outright take over full responsibility.
Communism is the state-of-affairs that never comes to pass because it is premised upon the idea that the Socialist state that owns and controls everything will “wither away” and voluntarily self-liquidate after it transforms people as Marx describes. (Note there are non-Marxist versions but these are almost trivial in their ongoing intellectual influence). “Communist” parties ran Socialist states with the ostensible goal of reaching communism, but of course the apparatchiks never had any real intention of putting themselves out of their jobs.
Note that most people define Socialism in economic terms, but while Socialists themselves, in their descriptions, originated this misconception, their interests were *always* primarily social and cultural – fundamentally transforming social relations. The economic aspect was just seen as the means for that. However, by the 1920s a lot of insightful people realized that 1) the economic predictions of Marx weren’t coming to pass but 2) they wanted the social transformation anyhow, this was their real goal and 3) it could be achieved via cultural means. So you get the strain of thought beginning with Gramsci et al, which transmitted itself to the U.S. via people like Erich Fromm, Theodor Adorno, Marcuse, et al: cultural socialism.
This has proven much, much more effective and is intellectually ascendent now. It’s a variant strain that allows itself to make a peace (of a modus vivendi sort) with bureaucratic-capitalism (the non-free market “mixed economy” we currently enjoy, with private ownership of property but under public control and direction) as a milk-cow to finance their social engineering schemes. (The later made them natural partners with the Progressive movement, so the two became inseparably intertwined).
This FEE Lecture by Bradley Thompson is pretty good on the inherent inhumanity of Marxism, despite it’s claims to and reputation of “at least they meant well, but it’s never really been tried.” Turns out it is the Marxist despots who understood it most fully and it was the most bloody of them that put it into practice most according to Marx’s original intent.
“Libertarian Socialism” is an oxymoron, probably the latest term-of-art for Left-Anarchists wanting to make themselves popular. At best it means Libertine Socialism, but it’s still everything for the mass, nothing outside the mass, nothing against the mass.