Tranches are a common way of structuring debt instruments, such as collateralized debt obligations (CDOs) and collateralized mortgage obligations (CMOs). They are created to finance large projects and can also be used to pool various types of debt. In essence, tranches are debt securities that are divided into smaller pieces, making them more marketable to investors who may be unwilling to buy the entire package.

Tranches have different maturities, and each tranche carries its own risk, yield, and priority in the case of default. In a CDO or CMO, for example, senior tranches would have a higher seniority than junior tranches and would get paid out first in the event of default.

The creation of tranches allows for the pooling of different types of securities, such as home mortgage loans and car loans, for instance. Mortgage-backed security (MBS) tranches can be further divided into classes depending on the risk.

The most well-known example of a tranche is the mezzanine tranche. This tranche sits between the senior and the junior tranches and may offer the highest coupon rate among the tranches. It is typically used to purchase higher-risk assets.

Tranches are often used in the context of structured finance deals. In a typical structured finance deal, a specific financial asset, such as a pool of mortgages, is pooled into a single security and then divided into tranches. Each tranche has its own characteristics and is often rated by a credit rating agency. The investors in the tranches purchase the pieces that meet their particular risk appetite and desired returns.

Tranches have become increasingly popular in the financial industry, as they offer an efficient way to spread the risk of a large, potentially risky loan. By dividing the debt into different sections and creating tranches, the lender diversifies the risk and can make a larger loan package more attractive to investors. Tranches also allow for an inherently complex structure to be divided into manageable pieces, allowing financial instruments to be split into different levels of risk.