Phishing refers to sending emails that allegedly come from reputable sources, with the goal to trick users into revealing personal, private or confidential information.
A reputable source could be (in relationship to the user):
A person in supervisor role, e.g., school principal, president of the company, etc.
An official, e.g., from IRS, police, etc.
Representative of a reputable company, e.g., Microsoft, Apple, Google
A familiar person, e.g., colleague
A person in power, personally unknown to the user, e.g., Bill Gates, King of Liberia, etc.
Attacker's goal: The attacker could seek to learn:
username and password for some service
SSN, address, phone number
bank information, credit card number
The attacker could also attempt to infect the user's computer with malware and steal information that way
Action plan: If you receive an email that looks like phishing take the following actions:
Do not click on any links in email
Forward the email to your IT administrator or flag the email as spam
Alert friends and colleagues that similar emails may reach them, and that they should be catious
Phishing is not limited to email: You can receive scam messages via text, app chat (e.g., WhatsApp, Facebook Messenger), in ads, in promotinal content on social network apps, via phone call, etc.
Phishing and scam are related: phishing usually seeks to steal information while scam seeks to steal money or sell you fake goods, but the line between two is thin and sometimes blurry.