Note that's a US definition — Europe is stricter and draws the line at non-public information [0], aside from certain carveouts and safe harbors. Matt Levine describes this as "theft" (misappropriating nonpublic information) vs. "fairness" (using nonpublic information at all) — iirc if you're on a flight and overhear a passenger in business class talking about an upcoming merger they're working on, that's legal to trade on in the US but illegal in Europe. At least that's what I generally remember about "parity-of-information" theory.
[0] https://blogs.law.ox.ac.uk/oblb/blog-post/2024/01/insider-de...