A clear, accessible breakdown of Reb Chaim’s famous chiluk between meivi tumah and chotzetz, explaining why hovering alone isn’t enough to block tumah without a true shem ohel. We then explore the Noda B’Yehuda’s landmark application to umbrellas on Shabbos, showing how “ohel” for Shabbos works differently than “ohel” for tumah — two systems, two definitions, one sugya made simple.