It is a light bulb. Inside of it, there is a “Y” sort of drawing to indicate the inner workings of the bulb. It also has the screwing part on the bottom of the bulb.
This Idea 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 15,800 icons, all in the same style and quality.