Clean is a word that serves as an adjective and a verb.
As an adjective, clean often means free of disrespectful, ignorant vulgarities. One's productivity, respect for others, and even intelligence can often be gauged simply by observing the vulgarities in his language.
Conservapedia is a clean source of information that encourages the users to provide insights and learn. The distracting and offensive crude language found on other sites does not infect or burden this site.