Monetary expense is basically a cash-money expense, so a non-monetary expense is an expense that isn't money. Some examples would be physical or personal expense.

If revenue (income of money) is a credit, then an expense (outflow of money) is a debit.

to spend money

In accounting an expense activity requiring someone to spend money. For instance, paying employees is considered an expense to businesses.

Actual expense is what something costs. Interest expense is what it costs to borrow the money for an actual expense. No one would borrow money to buy something if the cost to borrow the money was more then the cost of the thing they were buying. *I disagree; over the long run people pay more interest on their home mortgage than the initial cost of the home.