Which major dictionary made history in 2001 by adding the advertising slogan 'Where's the beef?' as an official entry, recognizing its evolution into a phrase meaning 'to question the substance of an idea or product'?

Marketing campaigns have the power not just to sell products, but to shape language itself. Throughout history, certain advertising slogans have been so impactful that they've entered our everyday vocabulary, transcending their commercial origins. This trivia question explores how a major dictionary publisher acknowledged this linguistic phenomenon with a groundbreaking decision about advertising language.

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Merriam-Webster Dictionary
Oxford English Dictionary
American Heritage Dictionary
Cambridge Dictionary