Fixed-Income Security

What Does Fixed-Income Security Mean?
An investment that provides a return in the form of fixed periodic payments and the eventual return of principal at maturity. Unlike a variable-income security, where payments change based on some underlying measure such as short-term interest rates, the payments of a fixed-income security are known in advance. 

Investopedia explains Fixed-Income Security
An example of a fixed-income security would be a 5% fixed-rate government bond where a $1,000 investment would result in an annual $50 payment until maturity when the investor would receive the $1,000 back. Generally, these types of assets offer a lower return on investment because they guarantee income.