Now that it appears likely that Joe Biden and the Democrats will inherit the White House it might be useful to keep in mind the distinctions between "liberals" and "leftists" or, as the latter are often called, "progressives."
President-elect Biden, who was once fairly moderate, has in recent years moved leftward and gained a reputation for being rather liberal/left. His party, however, is dominated by radical leftists who also exert an outsized influence in academia as well as news, entertainment and social media.
Given the dominance of leftist progressivism in the Democratic party and, indeed, in the culture as a whole, it'll be interesting to see how far Mr. Biden allows himself to be pulled toward their positions.
This five minute Prager U. video gives a succinct explanation of what those positions are and highlights the main differences between leftists and liberals:
One thing about these distinctions that should be kept in mind: Many people are liberal on some issues and leftist on others, so there's lots of ideological gray among folks on the left side of the ideological spectrum, just as there is among those on the right.