Definition
Plain language
A measure of how different two sets are based on what fraction of their items they share.
As stated in the literature
A set metric defined as one minus the size of the intersection over the size of the union, satisfying the metric axioms; used for fingerprint similarity in geometric memory substrates.
Also called: Jaccard
Why it matters: It's a simple, well-behaved way to compare sets — like document fingerprints or feature presences — without caring about counts or order.
For example, two recipes that share 4 ingredients out of a combined 10 have Jaccard distance 0.6.
Heard on the show
“And the distance metric they use is Jaccard — set intersection over set union, basically.”Episode 042 — An Agentic Scientific Computing System That Actually Remembers What It Learns