The phrase "big bro" is a short way of saying "big brother" and it typically refers to an older male sibling or a close male friend who provides guidance and protection. Full definition
Can't beat snorkeling with big bro @JordanSpieth in beautiful Maui! (sbnation.com)
Standard Sport report that Xhaka is currently training with FC Prishtina in a bid to maintain his fitness, although an alternative theory is that he had to return to Kosovo after Euro 2016 because big bro Taulant Xhaka was locked out of their mum's house and had been cowering on the front step even since Albania's group - stage elimination. (caughtoffside.com)