Rubbish is a synonym for garbage or trash. The word is more commonly used by speakers of British English than by speakers of American English.
The noun rubbish also means writing or speech that is worthless, untrue, or nonsense, especially in British English. Your teacher might tell you that your paper thesis is a load of rubbish if it states that Winston Churchill and Franklin Roosevelt were aliens sent from another planet to "fix" World War II. In British slang, rubbish is also a verb that means to criticize strongly. Don't be surprised when the professor rubbishes your paper — he's a well-known Churchill scholar.