Annoying phrase that many people on YouTube say to try to get people to subscribe to their channel. It works by guaranteeing that if someone subscribes to their channel, they will subscribe back. People do this to try to feel like they are important and so they can brag about how many subscribers they have. They also do this because they say that if you have enough subscribers, YouTube will pay them to make videos. It will never happen because most people do not care about the sub4subers. It has gotten so far out of control that some people have made accounts whose sole purpose is subscribing to people hoping that they will subscribe back. It usually doesn't happen.

sub4sub is a term used on the Video Sharing Website "YouTube"
to say "sub4sub" to another user means that if that user will sub (subscribe) to your videos, you will sub back to theirs, It may sometimes be posted as a comment on any random video to be pointed towards any user that's stupid enough to get sucked into it, Many sub4sub's are ignored, or marked as spam

A popular word among youtube users meaning subscription for subscription. People trade this like pokemon cards.

A popular phrase used on YouTube. When you ask someone for a sub4sub, you subscribe them, and they subscribe you, in result, both youtubers gain a subscription. Unfortunately, a large amount of youtubers that do this are kids who have awful videos or (god forbid) no videos. Those who have awful videos just want attention. Those who have no videos look like complete idiots each time someone sub4subs them, looking more and more like a chode. They have yet to realize this. It is rare when a person with good videos asks for a sub4sub, because they usually do not need it. These Sub4Sub whores are usually found on Fred's channel.

It's a term for use at Subway restaurant's, where one customer, who is generally not satisfied with his sandwich, asks another Subway customer if they would like to trade sandwich's of equal value.