Medium Term Notes (MTNs) are debt instruments typically used by banks and other financial institutions to raise funds. Here are some key characteristics of MTNs:

1. Maturity Period: As suggested by the name, Medium Term Notes usually have a medium-term maturity, which can range anywhere from one to ten years. This is in contrast to short-term instruments like Treasury bills (which mature in a year or less) and long-term bonds (which might have maturities longer than ten years).

2. Flexibility: One of the key features of MTNs is their flexibility. Issuers can tailor the notes in terms of size, maturity, and coupon structure (fixed or floating rate) according to their funding requirements and market conditions. This makes MTNs a very versatile tool for financial management.

3. Issuance: Unlike bonds, which are typically issued all at once, MTNs are usually issued under a "note program." Under such a program, the issuer can issue notes periodically, as and when needed, up to a certain total amount. This offers ongoing access to the capital markets and can be more cost-effective.

4. Investor Base: MTNs are typically sold to institutional investors through a private placement, and they might not be as liquid as other securities like government bonds. However, they often offer higher yields to compensate for this lower liquidity.

5. Credit Rating: The credit risk associated with MTNs depends on the creditworthiness of the issuer. Higher-rated issuers can typically borrow at lower interest rates.

6. Purpose: MTNs can be used by the issuing entity for a variety of purposes, including financing capital investments, refinancing existing debt, or general corporate purposes.

7. Regulation and Documentation: The issuance of MTNs is subject to regulatory requirements and involves detailed documentation, including the terms of the note, the issuer's obligations, and the legal framework governing the notes.

In summary, MTNs provide a flexible, customizable means for banks and other entities to raise medium-term funds, with specific characteristics that cater to both the issuer's and the investors' needs.