Opposite of expense? [duplicate]

Solution 1:

They are the same sort of liability, so there is no need for a term to distinguish them.

However, they are not both liabilities on the same set of books. The invoice you must pay is a liability (a payable) on your books, but an asset (a receivable) on your customer's books. Likewise, the invoice your customer must pay you is an asset (a receivable) on your books, and a liability (a payable) only on your customer's books.

Solution 2:

If someone has yet to pay a bill that you issued, this would be entered in Accounts Receivable or similar, where it is usually considered an asset rather than a liability.