Definition
Plain language
The most something could possibly be.
As stated in the literature
A provable or estimated ceiling on a quantity; reported here to flag that an effect size may be inflated by favorable experimental setup.
Also called: upper-bound
Why it matters: Labelling a number as an upper bound warns readers not to expect that result in practice, since the setup was chosen to give the effect its best possible showing.
For example, saying a method fixes "at most forty percent" of failures means forty percent is the ceiling under the most favorable conditions measured, not the typical result.
Heard on the show
“One more pushback worth voicing — the Cauchy-Schwarz bound is an upper bound.”Episode 010 — When Reward Climbs But Reasoning Goes Generic: Diagnosing Template Collapse in Agentic RL