It means the video has a resolution of 1920 pixels horizontally by 1080 pixels vertically.
Episode 1080+ (which usually falls into this season numbering) marks a pivotal moment in the series. After years of buildup, the battle against Kaido reaches its fever pitch. Fans seeking this specific 1080p quality are often looking to experience the revelations or the climax of the Onigashima raid in the best possible fidelity. One Piece-S20E42-1080p--HIN-ENG-JAP--PIKAHD.COM...