an illegitimate solicitation via email for personal information, disguised as coming from a legitimate source. They often ask for usernames and password. THESE MESSAGES SHOULD BE IGNORED AND NEVER RESPONDED TO. Phishing messages often have a hidden Reply-To address different than the sender address, to lure recipients into sending replies to a third party.
The email message may look legitimate (e.g., from your bank) but is really a type of social engineering attempt to acquire sensitive information, such as user ID and password, or to infect the target computer with malware.