Trash is rubbish or garbage — it's the stuff that gets thrown away. Your town might organize a clean-up day each year when people pick up trash in parks and neighborhoods.
Trash is dirty, worthless, leftover debris. Fittingly, the word is also a terribly derogatory term for useless, low-status people: "I should've known you were nothing but trash." And to trash talk is to brutally criticize or gossip about someone. You can even use trash as a verb, to mean "throw away," as in, "I'm going to trash this trash in that trash can over there."