A bond is a debt instrument issued by a company or government to raise capital. Investors who purchase bonds are essentially lending money to the issuer, who promises to repay the principal amount plus interest over a specified period of time.

Equity bonds do not exist. Corporate bonds are issued by companies, government bonds are issued by governments, and municipal bonds are issued by state and local governments.

Coupon bonds pay interest periodically, typically semi-annually or annually. Zero-coupon bonds do not pay interest periodically, but are instead sold at a discount to their face value. When the bond matures, the investor receives the face value, effectively earning interest over the life of the bond.

When interest rates rise, bond prices fall, and vice versa. This is because investors are less willing to pay a high price for a bond that is paying a lower interest rate than they could get from a new bond with a higher interest rate.

Credit risk is the risk that the issuer of a bond will default on their obligation to pay interest and repay the principal. This risk is typically measured by the bond's credit rating, which is assigned by a credit rating agency such as Moody's or Standard & Poor's.

A bond indenture is a legal document that specifies the terms and conditions of a bond issue, including the interest rate, maturity date, and payment schedule. It also protects the rights of bondholders by specifying the issuer's obligations and the remedies available to bondholders in the event of a default.

Callable bonds give the issuer the option to redeem the bond before maturity, typically at a specified price. Putable bonds give the investor the option to sell the bond back to the issuer before maturity, typically at a specified price.

Bond rating agencies assess the creditworthiness of bond issuers by evaluating their financial condition, management team, and industry outlook. They then assign a credit rating to the bond issue, which indicates the likelihood that the issuer will default on their obligation to pay interest and repay the principal.

Bond funds are actively managed by a portfolio manager who selects the bonds to include in the fund. Bond ETFs are passively managed and track a specific bond index, such as the Bloomberg Barclays US Aggregate Bond Index.

The best way to invest in bonds depends on your individual circumstances and investment goals. If you have the time and expertise, you can buy individual bonds. If you prefer a more diversified approach, you can invest in a bond fund or bond ETF.