There is a Pasuk in yesterday’s Parsha that says לא תלך רכיל, that one should not be a peddler of gossip. This is the source in the Torah for improper speech.
The Rambam in הלכות דעות fine tunes his definition of such speech into three categories: The first is רכילות which refers to simple true gossip about another person. It is not negative speech but just idle talk.
The second category is לשון הרע, which refers to true gossip about another person but negative. Such conversation makes that person look bad and is damaging.
The final category of the Rambam is מוציא שם רע, bringing a bad name on a person. Here lies are spoken about the person. And this is the most damaging speech of all.
We must follow the advice of the חפץ חיים and guard are tongues!