The decline in an ad's effectiveness that occurs when an audience has been exposed to it too many times, becoming less responsive even though the underlying targeting and offer haven't changed.
Why it matters
Ad fatigue is a normal, expected part of any sustained campaign — recognizing it early, through metrics like declining CTR at a stable frequency, lets a team refresh creative or adjust frequency caps before performance craters.
In a sentence
"Performance decline was gradual and correlated with frequency — a classic ad fatigue pattern, not a sign the offer itself had stopped resonating."
Related terms
Often confused with: Creative fatigue (largely interchangeable; see Category 2 entry for the specific distinction some practitioners draw).
Synonyms: Creative fatigue, banner blindness (a related but distinct phenomenon referring to users unconsciously ignoring ad-like content regardless of frequency).