on your keyboard - this hotkey takes you to the site search engines. The feature is unavailable in individual quizzes, puzzles and games, in forms, pop-up windows and a few more (logical) instances. The search hotkey is extra to other search features e.g. search query boxes.
Almost all pages have the hotkeys feature.
Details of the other 9 hotkeys at SITE TOUR or SITE HELP or SITE TIPS. Summary below:
Tip: save the above image for a quick reference.