For those who are unfamiliar with two-factor authentication, it means that in addition to your username and password, you will also need to enter an authentication code. This code is a one-time generated code that authenticates the user. This is similar to what some banks are doing with security dongles that generate said codes when attempting to login or make transfers.
This is also the same feature that Instagram will be using, except that users will be required to add and verify a phone number with the service, and should anyone else try to log into your account, you will be texted a code that verifies who you say you are. This is a feature that many have argued should have been implemented a long time ago.
In fact just a couple of years ago, Apple’s iCloud was compromised when accounts of celebrities were accessed illegally and private photos were stolen and published online. This resulted in Apple upping their security and implementing two-factor authentication on a wider scale. In any case for those of you who are particular about their Instagram account’s security, then this is a feature you’ll want to check out.