Full form of FD is Fixed Deposit

A fixed deposit is a form of risk-free savings instrument in which the investor/depositor deposits their money in a bank(preferred) or a regulated NBFC company for a fixed period (in days, months, or years) at a guaranteed interest rate. The interest earned by the principal amount can be credited on a monthly, quarterly, half-yearly, or yearly basis, with the flexibility to either re-invest or withdraw the generated interest. Re-investing the generated interest is recommended to take advantage of growth compounding.

FDs with an investment period of 5 and more years are also generally eligible for tax-saving.