An email address, often not actively used by a real person, set up specifically to identify senders with poor list hygiene — sending to a spam trap signals to mailbox providers that a sender isn't properly maintaining their list.
Why it matters
Hitting spam traps is one of the fastest ways to damage sender reputation and deliverability across an entire domain, which is why good list hygiene (removing old, unverified, or long-inactive addresses) matters even when it shrinks list size.
In a sentence
"We traced a deliverability drop back to a handful of spam traps that had accumulated in an old, unpurged segment of the list."