Other Japanese already answer for it "Keigo" if we say commonly Polite words (language)or respects words (language). You friend mean that words or language. The usage is really complicateed for non- native speaker. The words or sentance should make use differently. Those are classify Imperinal house hold words, repecptive word, polite word, anothers. This is not slang. this is one of Japanese language style.