What does 100% circulating supply mean?

Can you clarify for me the meaning of "100% circulating supply" in the context of cryptocurrency? I understand it refers to the total amount of a particular cryptocurrency that is currently in circulation and available for trading, but I'm not sure what it signifies when the percentage is at 100%. Does it mean that all the tokens have been mined and released, or is there something else I'm missing? Your insight would be greatly appreciated.