In the Rule of Saint Benedict, the term appears several times, referring to any superior, whether an abbot, provost, dean, etc.
[1] With the Cluniac Reforms, the term prior received a specific meaning; it supplanted the provost or dean (praepositus), spoken of in the Rule of St. Benedict.
Each of these was called circa (or circator), because it was his duty to make the rounds of the monastery to see whether anything was amiss and whether the brethren were intent on the work allotted to them respectively.
He had no authority to correct or punish the brethren, but was to report to the claustral prior whatever he found amiss or contrary to the rules.
[1] In some orders, like the Benedictines, a monastery remains a priory until it is considered stable enough and large enough to be elevated to the rank of an abbey.
Among communities of friars, the second superior is called the sub-prior and his office is similar to that of the claustral prior in the Benedictine Order.
These Grand Priories were joined into larger administrative units known as "Langues", which roughly encompassed all of the order properties within a single language sphere.
During the peak of the Orders' influence, the chivalric Grand Priors were considered to be equal in rank with a bishop.
Within the Order of the Holy Sepulcher, the title of Grand prior is held in personal union by the Latin patriarch of Jerusalem.