What do you call an unsolicited email message that masquerades as coming from a legitimate sender, and attempts to get you to disclose sensitive information or click on a link?

It is called Phishing

Explanation:

In computer security, phishing is an attempt by fraudsters to steal very important information from victims. These information most times are the login credentials such as debit/credit card details, usernames and passwords/PIN etc. Fraudsters carryout phishing by sending out messages (mostly electronic mails) to their victims, these messages appear as though they are genuine and official from institutions known to the victim (for example banks). Once the victim opens the email, he/she will be tricked to click on links that lead to the Phisher's website where sensitive information can be stolen.