In the context of US political system, it's opposite of "conservative". In the context of European politics, it's libertarian. In the context of leftist politics, it's "centrist", or rather "center-right".
While that helps, what doesn't help is that people don't often specify their context when they use it. An American commenting on Australian politics might very well use their own colloquial definition.
Things are even more complicated than that due to the existence of liberal anti-capitalists that interpret the liberal theory of inalienable rights, which originated in the abolitionist, democratic and feminist movements, as also invalidating the employer-employee contract.
In other words, there is overlap between liberals and leftists as well