Hollis is from the Old English holegn (holly grove) — a place-name and surname now used as a unisex given name. Hollis Mason — Nite Owl, one of the original Minutemen superheroes in Alan Moore's Watchmen (1986-1987); his memoir Under the Hood is one of the most-quoted passages in the graphic novel; the 2009 Zack Snyder film and 2019 HBO series both feature his character.
Hollis 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 Hollis reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.