Ah I see. That is actually the integration with 2 factor authentication in Joomla. It allows you to use apps like Google Authenticator to enter a code in order for you to be able to login.
Hello Mark,
Thank you for your answer.
I have validated this option to test, actually a code is well requested, but how do you get this code?
Google uses a sending by SMS, but how to proceed with EasySocial?
Joomla's 2 factor authentication doesn't use sms. You need to use apps like Google Authenticator or some other similar apps. You can learn more about 2 factor here, https://docs.joomla.org/J3.x:Two_Factor_Authentication