Original: The de Wahl's Rule is a rule of word formation, developed by the Balto-German naval officer and teacher Edgar de Wahl and applied in the artificial language Interlingue (also called "Occidental") which was also his creation.
Simplified: De Wahl's rule is a rule of word formation, developed by the linguist Edgar de Wahl and applied in a constructed language Occidental (known also as "Interlingue") created by him.