Two Factor Authentication
2FA (Two factor authentication) is a method of authenticating yourself on a device when you login to an account that may have access to sensitive information like banking information or private company data.
When using 2FA you will usually have another device setup as an authentication step so when you login from a device to an account, you receive a text or generate a code that is valid for a certain period of time (often a number of minutes). You need to enter this code to prove it's you logging in and not someone who may have gotten your login details.
Why does 2FA matter?
A common attack that is done on accounts that do not have 2 factor authentication is the attacker will login to the users email, send everyone in that persons address book an email with a link to a "document" which is not malicious in itself but when you open the document it sometimes leads to an "error" that says you cannot view this file and pushes you to click the link to login. Finally that leads to a phishing page which looks similar or tries to impersonate a legitimate login page like a bank or business system in order to grab your credentials and add you to the chain of victims.
If the account that was compromised had 2FA enabled it would be very unlikely that the attacker would have access to the code required to unlock or login to the account in the first instance. That means the attack is more or less stopped in its tracks and the users details are useless to anyone except the user themselves.