Outbound Glossary
Email verification
Checking an address exists before you send. It removes dead addresses, and it cannot tell you whether a person is worth writing to.
Verification asks the receiving server whether an address is deliverable, without sending a message. Done before a campaign it strips out the addresses that would have hard bounced, which protects your reputation.
Two limits worth knowing. It cannot answer for catch-all domains, and a verified address is not a verified person: someone can have left the company months ago and still have a live mailbox. Verification is hygiene, not qualification.