What does it mean for a sports card to be numbered 1/X?

A card numbered 1/X is the 1st copy out of its parallel's print run, where X varies by set and parallel. A 1/99 is the 1st of 99, a 1/25 is the 1st of 25, and so on. The /X notation is collector shorthand for "of any print run."

Why do collectors care about cards numbered 1?

The 1 numerator is the bookend of every print run, the very first copy produced. Collectors prize 1/X cards across all parallels because the "1" stamp signals the start of the run and often commands a premium over middle numerators of the same parallel.

How rare is a card numbered 1/X?

For any given parallel, the 1/X copy is one-of-one — only one card in the world carries that exact stamp for that print run. Across all sets and parallels combined, 1/X copies exist in larger total numbers because thousands of different cards are produced each year, but each individual 1/X card is unique.

How do I find cards numbered 1 on eBay?

eBay's title search misses most 1/X cards because sellers rarely include the exact serial in the listing title. SerialScout reads the serial number from every listing image and lets you filter by exact numerator. This page shows every active listing with a numerator of 1, across all print runs.