Bond
A type of investment in which you lend money to a company or government. In return you get interest payments and repayment of the money you lent at the end of a specific term. The interest rate and term are set at the start of the investment.
Investing in bonds is generally considered safer than shares. But there are still risks, primarily default risk (i.e. the company or government becoming insolvent), inflation risk, and the risk that interest rates rise over time.
A bond issued by the UK government is also known as a gilt. You can buy bonds directly, as well as invest in funds that hold bonds.