According to Webster's Dictionary, to "censor" means "to examine in order to suppress or delete anything considered objectionable."

When a government prohibits speech that is not obscene and does not incite violence, that is censorship. The First Amendment, which protects against government restrictions on or interference with the content of speech, applies to government at the national, state, and local levels, protecting the speech of public employees there.

In his first week in office, Trump began censoring the website of the Environmental Protection Agency and the Twitter accounts of the National Park Service.