It is the belief that one God compromises three persons
In christianity the Trinity is described as a mystery because it is impossible to fully understand it
The trinity is not specifically metioned in the new or old testament but there are many references in the Bible
an example of the trinity in the Bible?
At Jesus' baptism (Mark 11:11) Jesus himself is of course present; a dove which can be heard from Heaven saying 'you are my son, the beloved; with you I am well pleased'