Church has multiple meanings. It can refer to a single Christian house of worship, to the Christian Church as a whole, to a denomination, or to ecclesiastical authority.
As a denomination or the whole Church
In this context the term may be controversial. To Protestants, the Church is the whole body of Christian faithful. To Eastern Orthodox and Catholics, the Church is a single institution founded by Christ. Moreover, Catholic doctrine specifies that denominations lacking a priesthood based on apostolic succession are not technically "churches," but "ecclesial communities." However, they are acknowledged by Rome to be united with the Body of Christ, however imperfectly, through the sacrament of baptism.