What does "SQL Injection" mean?

SQL Injection:

SQL Injection attacks exploit vulnerabilities within SQL which might allow an attacker to interfere with the queries that an application makes to its database. These type of attacks typically let bad actors view data they are not supposed to be able to retrieve, such as passwords, personally identifiable information, and the like, or to install software they then use to create mischief or for malicious ends.

 Portswigger: SQL Injection