The WD Liability account refers to money owed to an outgoing member, as part of their withdrawal.
This is meant to be a reminder to the club that as of the valuation date (or the current date, if you are looking at account balances on the main Accounting/Transactions page), a withdrawal was started, but that a payment date either has not been entered, or has not yet happened.
A payment can be entered by going to the Members section/page, and looking for an option to complete a pending withdrawal.
In the online accounting, go to Accounting > Members, and look for the link to complete a pending withdrawal just above the list of current club members.
Keep in mind that the WD Liability Account is date sensitive, and it can show up if a payout date has been entered for some time in the future.
For example: Some clubs have it written in their bylaws that the club has 60 or 90 days to pay a member. If a Withdrawal is started on one date, and the payout date is put in for 60 or 90 days latter, any Valuation reports that happen before that payout date will have an entry showing a W/D liability account.