"Filthy language" refers to using vulgar, obscene, or offensive words and phrases. There are several synonyms for this term, including foul language, profanity, cursing, and expletives. Other words that can be used to describe this type of language include obscenity, vulgarity, and indecency. The use of such language is typically considered inappropriate and can offend or upset others. It is important to use tact and discretion when communicating to ensure that one's words are respectful and appropriate for the situation and audience.