A spam trap is created in a number of ways.
In any case, having spam traps on your list is a strong indication that you have not followed best practice when gathering or maintaining your list. Hitting some of these trap types can cause blacklistings which may result in your account being terminated. If you haven't been sending to your list for a long time, we require that you only use data gathered in the past 2 years.
Addresses hidden from normal view, so that only a robot could find them.
Addresses that have been inactive for a long time, that should have been removed by your bounce processes.
Addresses that unsubscribed from your emails to ensure you honor unsubscribe requests.