The definition
For a given company, the historical frequency and size of its stock's moves after earnings reports — how often it moved, and by how much — measured over its past prints.
How the count is made
The count is built from a company's own earnings history. Each past print contributes one observation: the release, and the move that followed it. The moves are classified by size and tallied — how many prints were priced, how often the move went beyond a given size, and the middle move of the set.
Nothing enters the count from outside the prints themselves: no options-implied estimates and no analyst consensus. The tally reports hit rates and medians rather than averages, and every quantity in it is a count over prints that already happened.
On a base-rate card
A company's earnings base rate is what its base-rate card summarizes. The card carries the count in three parts — prints counted, the share beyond the stated threshold, and the median absolute move — and the glossary entries for the hit rate and the median absolute move describe how each part is read.
What it is not
An earnings base rate is not a forecast. It describes the prints that already happened for one company and says nothing about the size or direction of the move after a future print.
It is not a grade of the company, and it is not a comparison between companies: each rate rests on that company's own prints, over its own history, counted the same way as every other rate in the set.