Question

Define annuity certain and perpetualty

Answer 1

a fixed amount of money that is paid to somebody each year, usually for the rest of his/her life

Answer 2

Hey friend
The annuity is for a fixed period, but Perpetuity is everlasting. In an annuity, the payment is made or received. Conversely, in perpetuity, only cash outflow is there. Future Value of annuity can be easily calculated which is not possible in case of Perpetuity.
Hope this helps you.