Shannon is from the Irish Sionann (the goddess of the River Shannon, Ireland's longest river) — from sen (old, wise) + an (one). Shannon Sharpe is male (NFL Hall of Fame). Shannon Beador (The Real Housewives of Orange County).
Shannon 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 Shannon reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.