Wikipedia Italian Speed Boats What Is An Impure Consonant Sound????? Help!! Italian Grammar?

What is an impure consonant sound????? help!! Italian grammar? - wikipedia italian speed boats

I started reading an article on Wikipedia about Italian grammar, and the state to speak of impure consonant! Please, please help!
I quote: "I have in front of a consonant before a consonant or unclean unclean (s + consonant, such ..) l ') before a vowel." And "One unclean before a consonant (s + consonant) z. .."
Please help thnks sooooooo much!
Oh, and do not say that Google has already done it!