MTG Keyword Rules — Comprehensive Rules Glossary

Hideaway is a triggered ability. “Hideaway N” means “When this permanent enters, look at the top N cards of your library. Exile one of them face down and put the rest on the bottom of your library in a random order. The exiled card gains ‘The player who controls the permanent that exiled this card may look at this card in the exile zone.’”

Previously, the rules for the hideaway ability caused the permanent to enter the battlefield tapped, and the number of cards the player looked at was fixed at four. Cards printed before this rules change had the printed text “Hideaway” with no numeral after the word. Those older cards have received errata in the Oracle card reference to have “Hideaway 4” and the additional ability “[This permanent] enters tapped.”