Pentesting, also known as penetration testing, is a security assessment, an analysis, and progression of simulated attacks on an application (web, mobile, or API) or network to check its security posture. The goal is to find vulnerabilities and address them before a bad actor can exploit them. Pentesting is a critical measure organizations should put in place proactively to prevent security breaches. Cobalt, where you have pentesting as a service, there can get a group of pentesters looking for flaws.
Source: https://www.helpnetsecurity.com/2021/05/05/how-modern-workflows-can-benefit-from-pentesting/