Spam is any unsolicited communication on the internet. Predominantly generated via email, when it is known as ‘junk email’, you can also receive other types via different media – for example, text message spam, instant message spam (sometimes known as 'spim') and social networking spam through Facebook messages.
Spam is essentially advertising for services or products through bulk-messaging, and is mainly harmless. But it can also be of a more malicious nature as part of an identity theft scam commonly known as phishing.