It's an icon with a paint bucket about halfway tipped over. There is liquid running out of the bucket because it is tipped partially over. There is a slash line running through the middle of the paint bucket starting at the top left through the bottom right.
This is the No Filling icon for Windows 10
. Here we go. Optimized for 32x32 px, these are the simplest icons in the line style. Downloadable formats are PNG and SVG, among others. Icons8 icon pack is unique in providing a huge number of icons designed by the same team of four designers who create the new icons every working day in the same style and with the same quality. Same cool as the Bat Face, huh.