High church refers to any church service that has a formal liturgy, often accompanied by elaborate rituals and an ornate church sanctuary.
The Roman Catholic Church, Eastern Orthodox Church, and some expressions of Anglicanism, Lutheranism, Methodism, and Presbyterianism can be deemed high church.
The opposite is low church, and it is often associated with congregationalist Churches, such as Baptist churches and Churches of Christ. Though these churches may have a standard order of service, rarely is it accompanied by the formality of high church services.