This Minus 1 Day icon is a responsive icon. This means that it's optimized for four resolutions, from tiny 16x16 until highly detailed 80x80. The style comes from the latest Microsoft Office, which makes it perfect for any Windows applications, in particular, those with ribbon toolbar control. Unlike other icon packs that have merely hundreds of icons, this monster icon pack contains 15,100 icons, all in the same style and quality.
It's what looks like a small, desktop calendar, with two rings on the top to change the date. It has "- 1d" meaning to subtract one day, written on the front of the calendar, to be an icon representing the subtraction of a day for other calendar purposes.