What does "belief system" mean? Is it even a common phrase?

Native speaker’s answer
Rebecca
Yes, it is! A belief system is a set of principles that form the basis of a moral code, philosophy, or religion. In Taylor Swift's case, she is using this term to describe the beliefs she had about the way she had to be or act in order for others to like or respect. Ex: The Sikh belief system is centered around peace, equality, and meditation. Ex: My belief system was influenced by my Christian upbringing.