What is a one-time password? Can't access my Square Enix account

I signed up to a SE account some time ago, it was the only time I logged in their account system. When I tried accessing it again yesterday to pre-order a game from their store it asked me to login with my SE account, which requires 2 passwords? I'm sure I signed up with 1 password, I even

SQUARE ENIX Support Center - FINAL FANTASY XI

Can't access my account? : r/ffxiv

Using a Square Enix Account, FFXIclopedia

SquareEnix Security Token available

Dragon Quest X PC Beta: Everything You Need to Know to Register, Install and Play (UPDATED)

Getting Started, Game Manual

SQUARE ENIX Software Token - Apps on Google Play

I can't log into Final Fantasy XIV and it's really quite frustrating.

FFXIV Account Recalled 3 Hours After Purchase - EpicNPC