Maysoon (ميسون) comes from the Arabic root meaning "graceful in motion" or "beautiful face." Maysoon bint Bahdal (c. 620-700 CE) was a Christian Arab princess who married the Umayyad caliph Mu'awiyah.
Maysoon 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 Maysoon reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.