Mainstream Christianity and Mainline Christianity are informal terms that are usually used to refer to the main branches of historical, Trinitarian Christianity: {article146|Catholicism}, {article1616|Eastern Orthodoxy}, {article589|Anglicanism}, and {article1477|Protestantism}.
Within these broad categories are hundreds of denominations and churches that vary significantly in beliefs and practices. When people use the term "Christian denominations," they are usually referring to these groups.