Enid is from the Welsh Enid — possibly from enaid ("soul, spirit, life"). Enid in Arthurian legend — wife of Geraint; their story is told in Tennyson's Idylls of the King (1859) — "Enid and Geraint" is one of the most-anthologized of the Idylls.
Enid 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 Enid reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.