Many reformed and presbyterian bodies use the phrase "system of doctrine" in their ordination vows. The particular branch of Christ's Church of which I am a minister has as its fourth ordination vow:
Do you believe in and accept the system of doctrine and the manner of worship set forth in the Westminster Confession of Faith, the Larger and Shorter Catechisms, and the Testimony of the Reformed Presbyterian Church, as being agreeable to, and founded upon, the Scriptures?
Since officers vow that they believe and accept the "system of doctrine" then we should know what that means. In volume 1, number 7 of the Blue Banner of Faith and Life, JG Vos was asked that very question:
Our Queries for Ordination we profess to accept the subordinate standards of the Church, including the Confession of Faith, Catechisms, Testimony, Covenant, etc. Yet The Testimony has been amended from time to time. If we accept it before an amendment is adopted which modifies its meaning in any respect, how can we then also profess to accept it after this change?
Here is part of Dr. Vos's answer:
In our Terms of Communion we acknowledge that the system of doctrine contained in the subordinate standards is agreeable unto, and founded upon, the Scriptures. In the Queries for Ordination candidates
are called upon to state that they “believe in and accept the system of doctrine" set forth in the subordinate standards “as agreeable to, and founded upon, the Scriptures”. The phrase “the system of doctrine” cannot legitimately be understood to mean every detail of doctrine, or every individual proposition, of the subordinate standards...
As a matter of fact the phrase “the system of doctrine” has a definite meaning. The system of doctrine set forth in our Confession of Faith, Testimony, etc., is precisely Calvinism, or the Reformed Faith, in distinction from contrary systems of doctrine which are set forth in other creeds of the post-Reformation era. These contrary systems of doctrine are Lutheranism, Arminianism, Socinianism and Romanism.
While our Testimony has been amended from time to time, it has never been changed in such a way as to alter the system of doctrine which it sets forth. That system of doctrine, in the case of all our subordinate standards, is unquestionably pure and undiluted Calvinism...
So the System of Doctrine that we profess to believe and accept is "unquestionably pure" and "undiluted Calvinism." It is a joy to know that in essence our ministers, elders, and deacons all profess the same "System of Doctrine."