An Application Security Assessment is performed either manually or automatically, generally continuing throughout the software development life cycle. It will typically include focusing on using secure protocols, performing defined security checks on application code, performing regular code assessments, and training developers on safe coding practices and common mistakes (OWASP Top 10). Web application security assessment are designed to continually monitor website security, helping to identify and protect against application vulnerabilities, and keeping supporting applications and underlying systems fully patched and up-to-date.
Source: White Hat Security
Additional Reading: Security Assessment Market Is Booming Worldwide