A reaction channel is where they break down the music, the most popular ones are about Hip Hop/Rap but some do other music and comedians. A real reaction channel is someone that hasn't listened to the music and they give they're opinion of the song and they usually try to break down the lyrics/bars because it's too fast for most people to catch the first time listening to the music. Some guys are better than others and some are just fun to watch because of the personality.

This guy is the most popular and has some funny videos. He's 90% rap/hip hop but he's making a living doing this and having a good time.

And it's a reason to listen to a classic song!!

OMG that was hillarious, lol.

LOVE AC/DC but was not too impressed with the commentary. I got bored with him pretty quickly. Sorry.

Small note, that's a Parisian audience. Moscowian one gets even wilder.