This is a lightbulb indication to show that the light is turned off. It shows a lightbulb, with a large bulbous circle at the top which tapers off onto the bottom, and there's a large X in the middle to indicate the light is off.
This Light Off 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 16,000 icons, all in the same style and quality.