"Everything" is search engine that locates files and folders by filename instantly for Windows. Unlike Windows search "Everything" initially displays every file and folder on your computer (hence the name "Everything"). You type in a search filter to limit what files and folders are displayed. "Everything" only indexes file and folder names and generally takes a few seconds to build its database. A fresh install of Windows 10 (about 120,000 files) will take about 1 second to index. 1,000,000 files will take about 1 minute.
Thanks to zoran for the update.