What is an OSC prefix?

I just downloaded Muse Direct on my ios and connected to Muse 2016 headband. I turned on streaming but I am not sure what to write in the OSC prefix. How do I get that?

Also, I want to control a game live using the headband. Is it possible to live stream data from the headband to my MacBook? if so - is using Muse direct the possible way to do it?