The plain-English version
Information crossing an evaluation boundary in a way that would not be available during real use.
Why it matters
It can make a system appear more accurate than it will be after deployment.
Let’s make it click
Near-duplicate examples from the same event appear in both training and test sets.
Vibe Bro’s heads-up
Removing the obvious answer column may still leave proxy fields, repeated entities, or future-derived features that reveal it.
The docs behind it
Documentation links checked .
Editorial review · October 28, 2026
Supported: Leakage includes repeated entities, future information, and near-duplicates, not only an explicit answer column.