A Spam trap is an email address used by an ISP to catch illegitimate emails and identify senders with poor email marketing practices. These include emails created for this purpose and old emails which have been reactivated and should no longer be present on any up to date mailing list. These addresses are not operated by humans and add no value to your list.
Sending to a spam trap can impact the reputation and deliverability of the sender. This could lead to emails being blocked or the sender themselves being blocked by the ISP who has set up that trap.
Formerly, blocklist was known as blacklist.