All my life, "sedition" has meant, as far as I knew, criticism of the government, possibly false criticism. Nor did I know of laws against it since around a hundred years ago or more.
Here is something saying sedition is:
"The federal crime of advocating insurrection against the government through speeches and publications."
https://www.law.cornell.edu/wex/sedition
Here is a part of the law that sounds like it's outlawing sedition even though it doesn't actually include the word: https://www.law.cornell.edu/uscode/text/18/2385
The significance, ultimately, is I'm suspicious that someone is pushing this term because they want to turn around and outlaw criticizing the government and say Democrats asked for it. Or, even if nobody has that plan yet, that using the term carelessly could invite it.
Here is the law against seditious conspiracy https://www.law.cornell.edu/uscode/text/18/2384
> If two or more persons in any State or Territory, or in any place subject to the jurisdiction of the United States, conspire to overthrow, put down, or to destroy by force the Government of the United States, or to levy war against them, or to oppose by force the authority thereof, or by force to prevent, hinder, or delay the execution of any law of the United States, or by force to seize, take, or possess any property of the United States contrary to the authority thereof, they shall each be fined under this title or imprisoned not more than twenty years, or both.