Addison is an Old English surname meaning "son of Adam" — itself from the Hebrew adamah (earth). Addison Montgomery is a major character in Grey's Anatomy (2005-2012) and Private Practice (2007-2013), played by Kate Walsh.
Addison does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Addison reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.