first name - Christian name - forename - given name
Your first name is the name that was given to you when you were born. Your first name comes in front of your surname.
At some point in the conversation Brian began calling Philip by his first name.
In British English, people sometimes use Christian name instead of first name. This use is rather old-fashioned.
Do all your students call you by your Christian name?
In American English, Christian name is not used.
On official forms, you are usually asked to write your surname and your first name or forename. Forename is only used in writing.
In American English, given name is sometimes used instead of ‘first name’ or ‘forename’.