viral marketing
noun/ˌvaɪrəl ˈmɑːkɪtɪŋ/
/ˌvaɪrəl ˈmɑːrkɪtɪŋ/
[uncountable]- a way of advertising in which information about a company’s products or services is sent by email or social media to people who then send it on by email to other people they know
病毒式营销（通过互联网用户之间的电邮进行广告宣传） Word Originfrom the idea of the information being passed on like a computer virus.