From ACT Wiki
1. Cash flow - equal periodicity.
A series of equal future periodic cash flows, starting exactly one period into the future.
2. Cash flow - variable.
More generally, any series of future periodic cash flows, either equal in amount or growing at a fixed compound rate per period, starting at a future date or already in payment, and usually ending at a later future date.
3. Periodic income.
Any financial arrangement in which a periodic income is paid to an individual, often as a pension.
An insurance contract purchased from a life assurance company that pays an income in exchange for a lump sum.
There are many variations on annuities, depending on the nature of the income stream.