Secure code review is a continuous improvement process that an organization goes through to identify and fix potentially risky vulnerabilities in the late stages of the development process. This could be due to poor secure coding practices by the developers responsible for writing the code. As the last threshold before an application moves to production / live environment, secure code reviews are an integral part of the security process. They serve as a sort of final "green tick" to assure you that the code is safe and that all dependencies and controls of the application are secured and functional.
We have a dedicated security assessments FAQ section. Read it here.