The circulating supply refers to the coins that are accessible to the public and should not be nonplused with the total supply or max supply. The total supply is used to quantify the number of coins in existence, i.e., the number of coins that already exist minus the coins that were burned. The total supply is the sum of the circulating supply and the coins that are locked up indeed. Meanwhile, the max supply quantifies the maximum amount of coins that will ever exist, including the coins that will be mined or made available in the future.
