Phishing is an attack form that is usually carried out by email. The term phishing is made up of the two words password and fishing which describes the basic concept. Attackers try to convince the user that the email has been send by a trusted organization. Most phishing emails fake emails from financial organizations like PayPal or banks but other services like social networking sites such as Facebook or MySpace are also targeted by phishers.
Links in those emails lead to fake websites that look like the original website. The only purpose of those fake websites is to catch the login data of the user who does not realize that the fake website is not the real one.