What the difference between expense and prepaid expense with example?

Expense is any cost that the firm incurs to earn the particular revenue. Most expense are required to be paid except for a few "non-cash expense" such as depreciation.

Prepaid, as suggested, are expenses paid in advance but have not yet "used" to generate revenue. It is to be used at a later date. One example of a prepaid expense would be rent i.e. prepaid rent. The owner pays the rent for the next 2 months at $100 per month.

Prepaid rent = $200.