SQL Injection is a web security vulnerability that allows attackers to interfere with a website’s database queries by injecting malicious SQL code into input fields. This often happens when user input is not properly validated or sanitized. For example, an attacker could input a specially crafted SQL statement into a login form to bypass authentication or retrieve sensitive data like usernames and passwords. SQL Injection can lead to data breaches, unauthorized access, or even deletion of entire databases. Preventing it involves using parameterized queries, prepared statements, and input validation.