Definition: Account Balance (Net Liq.)
This value represents the current market value of all of your holdings + cash balance. It is supposed to indicate the estimate of how much cash you will have if you liquidated every position at the moment. Your brokerage platform may call it "Net Liquidating Value" or "Total Account Balance" etc.. Take the one that represents the total value of your portfolio and live-ticks with the market.
When tracking account balance, using this number is the most accurate representation of your performance/returns.