Why does X mean close?
[x] is a true icon, not representing a letter but representing an action, and only adopted to represent 'close' well after the development of graphics-oriented operating systems. The first appearance of [x] in GUI design was likely the Atari TOS, possibly influenced by the Japanese batsu and maru conventions.
What is the x icon?
X-Icon Editor is the first HTML5 application that allows you to create high resolution icons directly from within the browser. Windows Internet Explorer 9 introduces pinned sites, a feature with which you can integrate your websites with the Windows 7 desktop.