What is the maturity date of an ETN?

Excuse me, could you please clarify what exactly is the maturity date of an ETN? I understand that ETNs, or Exchange Traded Notes, are a type of debt security that track the performance of an underlying asset or index, but I'm a bit confused about the specific term "maturity date" in this context. Is it the date when the ETN expires, or when the issuer is obligated to pay back the principal and any interest or gains to the investor? Could you elaborate on this, please?