Phishing is a method of identity theft which requests confidential information such as usernames, account numbers, passwords, etc. by masquerading as a legitimate, trusted company. This term typically refers to attempts through email. However, this same type of attack can occur in person (social engineering) or over the phone (farming).
Phishing emails have become very sophisticated. It used to be that they were so poorly written that you could just rely on really bad grammar or spelling errors to determine their legitimacy. That is no longer the case. The emails can appear to come from trusted addresses and cleverly designed with graphics, disclaimers, etc. So how can you determine if an email is legitimate?