What is Certificate of deposit?

A document (often in the form of a security) confirming that money has been placed with a bank for a certain term and that at the end of that term the deposit amount will be returned with the agreed interest. It resembles an ordinary term deposit: the term and the interest are set in advance, and the interest is usually fixed. Withdrawing the money before maturity is often associated with a penalty or giving up part of the interest. Some certificates can be transferred to another person before maturity; this possibility is written in the terms of issue, so the terms should be read before buying.

Source: Investor.gov glossary: certificate of deposit; Merriam-Webster: certificate of deposit