It's more of a vibey term, and as such it is genuinely very difficult (perhaps impossible even) to concretely determine whether an LLM possesses consciousness. LLMs successfully express a lot of consciousness-like traits.
At some point you have to ask the question: does it even matter? If an LLM can sufficiently mimic consciousness, isn't that sufficient for us to treat it as conscious, even if it is in-fact not conscious (especially because we don't actually know)?