‘Boro’ is a popular term on Twitch which has it’s origin in the life mod Arma III. ‘Boro’ was first introduced in early 2015 on Lirik’s Twitch stream when the characters Lo Chang and Sayeed Black were saying ‘bro’ in the game Arma III Life. Due to thier accent they said ‘boro’ instead of ‘bro’ though.
Soon the term ‘boro’ spread on the entirety of Twitch.
Related links:
http://www.twitch.tv/lirik
http://www.twitch.tv/assassino___
http://www.twitch.tv/sayeedblack