Definition: Daily Expected Range
The standard deviation of the last 30 Daily Returns from account balance entries. It is only "Daily" if account balances are entered daily. If you enter them weekly, for example, this would be your weekly expected range.
A standard deviation, or expected range, means the actual number should fall within the range 68% of the time. So in this case, based on your previous account movement, you can expect your Account Balance (Net Liq.) to have a Daily Return within this range on 68% of days.
Ultimately, it's a great risk measure to compare to other traders or across your multiple accounts if account balances are entered consistently. Just make sure whatever your comparing is also entered daily (same interval).