It means a cool dude that is cool
Look at that Bruh over there! He lookin' fine!
Usually use by teenagers and express lack of interest to someone. Could balai mean “whatever”
How are you today?
Bruh!
Bruh when taken on its own means nothing, it is entirely dependant upon the context of a situation for meaning. It's similar to something like an exclamation mark, or using all caps in that way. Using it in a sentence, or even just on its own, typically adds some kind of emotion of confusion or disbelief to a statement. For instance, "what?" can have many meanings based on context, but saying "bruh what?" specifically implies that the cause for confusion was because the original statement itself made no sense.
"What is Obama's last name?"
"Bruh
"Bruh I got an A on that essay"
"Enjoy your meal"
"You too"
"Bruh"
It is a word commonly used to refer to a friend mostly towards a male, or an expression towards an illogical or horrendous situation, question, sentence, etc., it's use started around the early 20th century originating from the English word brother, used often by African American's slowly turning into 'brer' and 'brah' and now as 'bruh'.
E.g.,
Tommy: My bicycle was stolen so I had to take the subway and arrived late for class.
Charlie: Bruh.