its technically all Office 365, but there is Outlook Classic(the one that has been around forever and downloads your email into a OST file), New Outlook(which is basically just like an app on your phone and is a GUI representation of OWA) and then OWA(signing in through a browser.) Outlook Classic has way more issues than New, and i think it's primarily because it downloads all your emails to the computer for offline use, the someone complains about it being slow and i just recreate the Outlook profile. Outlook Classic is way better when it's not using on-prem Exchange, which is usually the case anymore. New Outlook might not need a license though, im not positive on that.