Two-step verification, or sometimes called two-step authentication, is an additional security feature designed to prevent anyone from accessing or using your account, even if they know your password. It adds an extra step to your basic log-in procedure. The single factor of authentication requires your password to log-in. The second factor requires you to enter a unique security code. Two-step verification makes your account more secure than not having one, but it is not perfect. It is widely used to add a layer of security to your online accounts.
In an article "Two-factor authentication: How and why to use it" by Matt Elliot from CNet.com, "Two-factor authentication requires two ways of proving your identity and can also be used to protect your various online accounts. It doesn't offer perfect security and requires an extra step when logging into your accounts, but it does make your data more secure online."
Source: Matt Elliot, March 28, 2017. ""Two-factor authentication: How and why to use it".