Nest is the medieval Welsh form of Agnes — meaning "pure." Princess Nest ferch Rhys (c. 1085-1136), called the "Helen of Wales," was the famously beautiful daughter of the last king of Deheubarth — through her descendants run the FitzGerald dynasty and many Welsh-Norman royal lines.
Nest is rare but iconic in Welsh history.
Nest 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 Nest reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.