OWASP Top 10

The OWASP Top 10 is an awareness document describing the categories of web application risk that appear most often.

It is not a standard, not a checklist and not sufficient as a testing scope, and it is regularly used as all three. As a way of teaching people the shape of the common problems it is excellent; as an assertion that an application is secure because it addresses all ten, it is not what the authors claim.