48 Across

NYT Daily • August 30, 2025

Library catalog ID

Answer:

ISBN

Hint:

Not available

Explanation:

A library catalog ID often refers to a unique identifier for books, and the most common one is the ISBN, or International Standard Book Number. It’s a numeric code that helps libraries and bookstores track and organize titles. The clue is straightforward—no wordplay—just pointing to the standard system used worldwide for book identification. Think of it like a book’s fingerprint.

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