The unavailable balance is your stock market value fund, and the available balance is that you can take it out or continue to buy stocks. Availability means that funds can be used to buy stocks on the same day, but they cannot be withdrawn through bank-securities transfer. That's the money after selling stocks that day.

The fund balance indicates the amount of funds that you can freely flow in your current account. The available balance should include some corresponding service fees and other non-current funds, which cannot be used as trading funds.