It's subjective and context based, on a person to person basis and in the aggregate societal norms.

It's the same as if you were talking about whatever broader group you were personally into. Just with the erotic attraction part removed.

If you, personally, have no criteria for judging you can try and work with what you understand the conversation partners tastes to be.

If you are talking to someone you think appreciates Hollywood hot then you can way "they are hot" with the understanding that you are commenting from a shared context of hot.

If you were to say "I think they are hot" that's a different context and implies you, personally, think they are hot.

To be clear, neither of those explicitly states an erotic attraction, though it can be taken that way, depending on the context.

Communication is hard.