OWASP Top 10

The Open Web Application Security Project (OWASP) Top 10 is a regularly updated report outlining the most critical security risks to web applications.
Its primary objective is to raise awareness about application security by identifying some of the most critical risks facing organizations. The report is created by a team of security experts from around the world and is widely recognized as the first step towards more secure coding practices.
OWASP Top 10:2021
OWASP Top 10
My opinion: The OWASP Top 10 is a useful reference for common web application security risks.
You will see it referenced in system requirements, pentests scopes and also in interviews. Because of this, I recommend you learn it in detail. As a security practitioner there’s no excuse for not understanding the entire list in detail due to it’s popularity and the fact that all of the content is basic/fundamental. One more thing to note is that the document is not comprehensive and shouldn't be used as a complete reference for your security strategy or system security requirements.

How to use the OWASP Top 10