Explanation:

- Subscription: A regular payment made by members or users for continued access to a service or organization. It is considered income because it generates revenue for the providing entity.

- Donation: A voluntary gift given by individuals or organizations, often used as income, especially for non-profits or charitable entities. It helps in funding operations or specific causes.

- Sale of Ticket: This is income derived from selling tickets for events or services. It serves as revenue for the organizing entity.

- Endowment Fund: A pool of money that is invested to generate income, but typically the principal amount is not used. Only the income generated from the investment is used. Thus, the fund itself is not directly income.