Active Addresses is a count of the addresses that were party to a transaction in the last 30 days in the ledger. High Active Addresses show high market participation and are generally considered a healthy sign of liquidity. On the other hand, low Active Addresses show reduced market participation and are generally considered a sign of falling liquidity.
An address is considered active as soon as it becomes a direct participant in a successful transaction — either as a sender or a receiver. As a result, active addresses serve as a good indicator of daily users over any particular blockchain.