See: <https://en.wikipedia.org/wiki/Libertarianism#Etymology >

The term "libertarian" was invented by Joseph Dejacque, who was, broadly, a communist who rejected using a centralized state to move society toward communism (this is the opposite of what we now call authoritarian communists, who believe that you have to seize state power first in order to bring about a socialist and then communist society).

in the 1960s Murray Rothbard, a right-wing libertarian, popularized the term to refer to people who want zero or minimal state power and want a sort of hyper-capitalism to run everything by contract. He wrote that he specifically chose to steal the term from the left. This is considered right wing because it will make hierarchical systems, especially capitalism, much more intense and brutal. The state doesn't usually limit the brutality of capitalism or other hierarchies, but from time to time popular movements have been able to make it do that.

In the US, most people will think you mean the Rothbard definition if you just say "libertarian" and will not really know what a "libertarian socialist" or "left-libertarian" is. American socialists will often have heard all of these terms.