Church - A medium-sized building in which Christians worship.
Denomination - Also called "Church" by Anglican, Catholic, and Orthodox traditions. This is a sect of Christianity.
Christianity and Communion of Saints - The church established by Jesus Christ and spread by Peter, Paul, John, and the Apostles thousands of years ago, and the mystical connection between Christians. Any believer is part of the body of the Church, the bride of Christ.
Worship Service, Mass, Divine Liturgy - The service where Christians gather and worship God as a congregation and perform certain ceremonies. This is commonly called "going to church" by most Protestants, though the more correct term is "going to be with church," since the church is not a building, but rather the various people who are disciples of Christ. (Not the sect)