Windows Search allow a user of the Windows operating system to find items like files, folders and programs that are on the PC or on networked locations.
The feature has been a default component of Windows since Windows XP. Only since Windows Vista has there been a default setting to crawl and index files similar to an Internet search engine. For Windows XP there is Windows Desktop Search available for download from Microsoft. It adds the indexing feature to XP.
Using the windows-search tag is preferred to using the search tag because it is more specific and allows users to find relevant questions and answers more quickly.
Windows-Search should be used for all questions pertaining to enabling, disabling, modifying the index and search function or how to effectively execute a search query. It should be used for any version of Windows. It may be used for windows-desktop-search.
More detailed information is available on Wikipedia.