Its source is an English expression meaning "A triad."
This girl's name is used in English and Spanish.
The name Trinity ranked 68th in popularity for females of all ages in a sample of 2000-2003 Social Security Administration statistics and 2406th in popularity for females of all ages in a sample of the 1990 US Census.
In Christian doctrine, God is held to be a single entity manifested in three ways: as Father, Son and Holy Spirit. This name is probably given with that doctrine in mind.