It's a logo of the flag of the United Kingdom. It's a rectangle with a cross in the middle then another thinner cross outlining that with lines going diagonally out of it to the edges too.
This Great Britain 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 15,900 icons, all in the same style and quality.