SQL injection (SQLI) is a type of attack where an attacker injects malicious SQL code into input fields or parameters of a web page, which is then executed by the underlying database. This attack method exploits vulnerabilities in input validation to gain unauthorized access to or manipulate the database.

An example of SQL injection would be if an attacker enters an SQL command like "OR 1=1" into the username field of a login form. If the web application is not adequately protected against SQL injection, the attacker could successfully log in because the injected SQL command causes the query to always evaluate to true.

SQL injection can have various impacts, including:

1. Disclosure of confidential information from the database.
2. Manipulation of data in the database.
3. Execution of malicious actions on the server if the database supports privileged functions.
4. Destruction or corruption of data.

To protect against SQL injection attacks, web developers should employ secure programming practices, such as using parameterized queries or ORM (Object-Relational Mapping) frameworks to ensure all user inputs are handled securely. Additionally, it's important to conduct regular security audits and promptly install security patches.

Amazon RDS stands for Amazon Relational Database Service. It's a managed service provided by Amazon Web Services (AWS) that allows businesses to create and manage relational databases in the cloud without having to worry about the setup and maintenance of the underlying infrastructure.

RDS supports various types of relational database engines such as MySQL, PostgreSQL, Oracle, SQL Server, and Amazon Aurora, giving users the flexibility to choose the database engine that best suits their application.

With Amazon RDS, users can scale their database instances, schedule backups, monitor performance, apply automatic software patches, and more, without dealing with the underlying hardware or software. This makes operating databases in the cloud easier and more scalable for businesses of all sizes.