Phishing is a very serious crime. It involves attempting to acquire  information such as usernames, passwords, and credit card details (and sometimes, indirectly, money) by pretending to be a trusting entity.
It was reportedly first used in 1995. There are several different phishing techniques that can be used. 

1. ^ "What is spear phishing?". Microsoft Security At Home. Retrieved June 11, 2011.

1. ^ "Fake subpoenas harpoon 2,100 corporate fat cats". The Register. April 17, 2008. Archived from the original on 2011-01-31.

Phishing

Phishing is a way of attempting to acquire information such as usernames, passwords, and credit card details by masquerading as a trustworthy entity in an electronic communication.

Spear Phishing

Phishing attempts directed at specific individuals or companies have been termed spearphishing. Attackers may gather personal information about their target to increase their probability of success.

Clone Phishing

A type of phishing attack whereby a legitimate, and previously delivered, email containing an attachment or link has had its content and recipient address(es) taken and used to create an almost identical or cloned email. The attachment or Link within the email is replaced with a malicious version and then sent from an email address spoofed to appear to come from the original sender. It may claim to be a re-send of the original or an updated version to the original.

This technique could be used to pivot (indirectly) from a previously infected machine and gain a foothold on another machine, by exploiting the social trust associated with the inferred connection due to both parties receiving the original email.

Whaling

Several recent phishing attacks have been directed specifically at senior executives and other high profile targets within businesses, and the term whaling has been coined for these kinds of attacks.