What is the trinity?

The word trinity is not found in the Bible, but the concept of one God in three distinct persons (not three gods) is.  We know that there is only one God as the Bible says (Deuteronomy 6:4).  We also know that Jesus was not only the Son of God but God in the flesh as well (John 1:1, 14).  The Holy Spirit is mentioned as being God throughout scripture as well (Acts 5:3-4).  The Bible very clear that all three are God, but they are all separate Persons as seen in scripture.  When Jesus (God the Son) was baptized, God the Holy Spirit came down upon Him and God the Father spoke from Heaven (Matthew 3:16-17).  The Bible also tells us that there are three that bear record in Heaven:  the Father, the Word (Jesus), and the Holy Spirit and that these three are one (1 John 5:7).  This is a hard concept to fathom, but it is a core doctrine to our faith.