Usually refers to desktop wallpaper, or having the dimensions large enough to be a desktop background. Common sizes are:

• width:1024 height:768
• width:1280 height:768
• width:1280 height:800
• width:1280 height:960
• width:1280 height:1024
• width:1600 height:1200
• width:1680 height:1050
• width:1920 height:1080
• width:1920 height:1200

(Copied from Danbooru.)

Wallpapers are not the main focus of this site. If you want to post many wallpapers, they may be better suited for Konachan.