Referential indeterminacy is like playing a guessing game when someone says something but doesn't give you enough information to know exactly what they are talking about. Let's say your friend says "Can you pass me the thing?" but there are three different things on the table. You would need more information to know which thing they are talking about. That's like referential indeterminacy - when someone uses a word or phrase that could refer to more than one thing and you don't know which one they mean unless they give you more information.