What does this representation of organic aromatic compounds mean?
This is the cyclooctatetraene dianion. One way to get to it is to start with cyclooctatriene and remove one hydrogen ion each from the two $\ce{- CH2 -}$ groups. This is related to the cyclopentadienyl anion, the more common aromatic anion.

Image source: https://www.masterorganicchemistry.com/2017/05/17/frost-circles/