Outstanding expense are those expense which are due but not paid and to be added with the respective expenses head and shown as liability in the balance sheet.Any amount which is due to a person against which the services are already provided for is an outstanding expenses. These are personal account but put together clubbed and considered as representative person account.

Nominal account is an account which is related and associated to losses, expenses, income and gain. But Outstanding salary is a personal account because it relates to actual persons. As the salary is due but not yet paid, so it doesn't come under nominal account.