Available balance is your token balance that is available for new orders on The Ocean.

When you place new orders on The Ocean, your available balance for the maker token will decrease. Then as your orders are settled, canceled, or removed from the book, your available balances will increase back towards the real token balance in your wallet.

Please note: For the ZRX token, your available balance will also take into account fees committed to being paid in ZRX for all outstanding orders.