Authorized simulated attack on a system to find security vulnerabilities. Like hiring friendly burglars to test your security system and find weaknesses.
Companies hire ethical hackers to perform penetration testing on their web applications before going live.
Penetration testing is a security practice, not a single cloud service. All major cloud providers allow it under specific rules (scope, authorization, and safe testing). Providers offer security tooling (logging, vulnerability scanning, WAF, IAM) that supports pen tests, but the test itself is typically performed by your internal team or a specialized third-party.