The breadth of definitions and their mis/re-interpretations from one team to another can cause confusion.

There are some foundation principles that are unshakeable (test at different layers of the system, run Continuous Integration/Deployment, ensure requirements are clearly defined) but some can be downright confusing (e.g. Component vs Component Integration, Functional vs Functionality).

I don't believe a qualification is any replacement for experience at the front line, but the ISTQB Exam Certification site offers concise definitions for many testing terms and offers many other useful resources. For example, their Seven Principles of Testing:

1) Testing shows presence of defects 2) Exhaustive testing is impossible 3) Early testing 4) Defect clustering 5) Pesticide paradox 6) Testing is context depending 7) Absence–of–errors fallacy

What are the principles of testing?