As posted on BBC...
The doctrine of the Trinity is the Christian belief that: There is One God, who is Father, Son, and Holy Spirit.
Other ways of referring to the Trinity are the Triune God and the Three-in-One.
The Trinity is a controversial doctrine; many Christians admit they don't understand it, while many more Christians don't understand it but think they do.
In fact, although they'd be horrified to hear it, many Christians sometimes behave as if they believe in three Gods and at other times as if they believe in one.
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