A 'Feature Reel' is a horizontal reel that operates independently of the main vertical reel grid. It doesn't create payline wins on its own; instead, it spins at the top or bottom of the grid and interacts with it. The primary purpose of the Feature Reel is to act as a trigger: when a symbol on it 'matches' the symbols on the vertical reel it's paired with, it activates a powerful bonus, such as turning all matching symbols into Wilds or Coins.