Iscah (יִסְכָּה) means "watchful" or "one who looks forth" in Hebrew. In Genesis 11:29, Iscah was the daughter of Haran (Abraham's brother) and sister of Lot and Milcah — Jewish tradition identifies her with Sarah herself.
Iscah is the etymological source of the English name Jessica (via Shakespeare's Merchant of Venice).
Iscah 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 Iscah reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.