a statement of the beliefs and principles held by a group, political party, or religious institution;
e.g. The doctrine of the Catholic Church is set by the Pope.
(noun)
a teaching, or a statement of the principles used in a branch of study/knowledge;
e.g. This is the most fundamental doctrine of my field of study.
(noun)
in American usage, a declaration of a fundamental government principle or policy, especially in areas such as military affairs or international/foreign relations;
e.g. The party released its doctrine containing changes to its international policy.