Un•der•ground (un’der ground’), n., adj.

1) A genre in music and other forms of media intended for an elite audience, that is often characterized by its high levels of originality and experimentation, and does not conform to typical standards, trends, or hypes as set by the popular mainstream media.

A buzz word being used to refer to creators and influencers forming or encouraging unhealthy relationships with their fans. Usually used in the context of young audiences feeling they have a relationship with the influencer due to the huge amount of the influencer’s content they consume. The influencer in question, however, is unaware of the fan’s existence other than the general knowledge of having fans. Common examples include Dream and his stans. These relationships are exacerbated by the influencers confirming they have more than a creator-to-viewer relationship.

The word is circulating due to various YouTube essays about the phenomenon using the word, and therefore people who enjoy complaining about influencers repeating what they heard in the video in any comments section they can find.

A movement or a group of people related to music, who do it not for the money, the notoriety or the fame, but for the love. They don’t promote, because they don’t crave popularity. They also don’t need to tell everyone about how underground they are because they aren’t really interested in labelling their own movement, they just do it, and if people enjoy it, great.

Art, opinion or organization that exists outside of mainstream society or culture. Also known as "independent" or sometimes "counter-culture".

The London railway system. Also called the Metro or Tube.

Underground is about passion. of course the word is missused and abused . a true underground artist will create music/art from the heart as apposed to something tailored to a commercial market.an underground event organiser will still put on the event for the love of it even if its going to lose money... underground artists can have a long career out of the often distructive gaze of mainsteam media and earn money which is closer to someone with a good job than the millions of there commercial counterparts. where as a commercial artist will probably have a short shelf life

in simple terms,
the opposite of mainstream