Sacerdotalism (from the Latin sacerdos - priest) is the belief in a priestly system where the priest has been given the special authority to act as a spiritual mediator between God and mankind. The Roman Catholic, Eastern Orthodox, and high Anglican traditions are sacerdotal. Although the priests are not supposed to be seen as better or more godly than others, their role in the sacraments of the church give them a special "mediatorial" role, as representatives of the Church (Christ's body on earth) and thus of Christ. This is especially noticeable in the Roman Catholic confession, mass, and last rites.
In Protestantism, if we except high Anglicans, there are no earthly "mediators," because each believer has the Holy Spirit in them. The Reformers rejected the sacerdotal system altogether, and substituted for it the general priesthood of all believers, who have direct access to Christ as our only Mediator and Advocate, and are to offer the spiritual sacrifices of prayer, praise, and intercession.
As the apostle Paul said, "there is one God, and there is one mediator between God and men, the man Christ Jesus," (1 Tim. 2:5 ESV).