SQL Injection is a common web application vulnerability that allows attackers to manipulate and exploit the underlying database. In-band (Classic) SQL Injection involves directly injecting malicious SQL statements into user inputs, resulting in the execution of unintended database queries. Inferential (Blind) SQL Injection occurs when attackers cannot see the direct results of their injected SQL statements, but can infer information based on the application's response. Out-of-band SQL Injection leverages a separate communication channel to extract data from the database, often using DNS or HTTP requests. Understanding these different types of SQL Injection is crucial for developers and security professionals to implement robust defenses and protect against potential breaches.