A spammer is a person who sends out spam mails and thereby gains an advantage.
A spam mail is an unsolicited e-mail that contains an advertising message or serves a manipulative purpose. For example, the spammer may use such an action to try to manipulate search engine results or to advertise products and services, bypassing the advertising opportunities offered in newsgroups and discussion forums. Spammers can abuse online media for their own purposes, but they can also be active as telephone spammers.
Spammers usually send several million spams to e-mail addresses and assume that a small percentage or per thousand will respond to the advertising message.