POMIS, or Post Office Monthly Income Scheme, is a savings scheme where you deposit a lumpsum for a fixed 5-year tenure, and in return you receive a fixed monthly interest payout directly into your account for those 5 years, with your original deposit returned in full at the end of the term. It's designed purely to generate a predictable monthly income stream, rather than to grow your capital.
There's a maximum investment limit per account (higher for joint accounts), and the interest rate is set by the government and reviewed quarterly, though your rate stays fixed for the entire 5-year tenure once you invest. The interest you receive each month is fully taxable as per your income slab, and there's no Section 80C benefit on the initial deposit. POMIS is popular with retirees and conservative savers who want a simple, government-backed, predictable monthly cash flow.