Rebound effect
Etymology
From "rebound" (Old French "rebondir," to bounce back) and "effect." The idea traces to economist William Stanley Jevons, whose 1865 "Jevons paradox" observed that more efficient coal use increased, not decreased, total coal consumption.
noun phrase · /REE-bound ih-FEKT/
When gains in efficiency are partly cancelled out because cheaper, cleaner use encourages more use.
What it names
Explains why efficiency doesn’t always save what it promises — a fuel-sipping car may just get driven more.
Example
After switching to LED bulbs, they left more lights on — the rebound effect ate part of the savings.
Related idea
The Jevons paradox is the extreme case, where efficiency raises total use outright; the rebound effect is the milder, more common erosion of expected savings.