I typed "Finder" in Spotlight. Finder isn't shown. Why? I use Mac OS X 10.9 (Mavericks)
On Mac OS X 10.10 (Yosemite) typing "Finder" in Spotlight does display the finder app.
Because Finder is located inside /System/Library. (Specifically, at /System/Library/CoreServices/Finder.app.) Everything inside any of the Library folders is considered a "system file", and not normally visible.
Interestingly, Yosemite seems to have made an exception for /System/Library/CoreServices, treating it more like an applications folder than a library folder. Spotlight will show Finder in Yosemite.
In a Finder search window (which is basically Spotlight with more focus on finding files but little or none on finding non-files), you need to add a
[System files][are included] search term to see system files. If you don't see
System files as an option in that first menu, select "Other..." and find "System files". (Note that you can search for it!) For future convenience, put a checkmark on it to add it to the menu.
What are you trying to accomplish? Finder.app is hidden. If you wish to quickly open finder, command-tab is easy.
If that's your goal, some of these suggestions may be helpful. Personally I use finder windows accessed via command-tab. I dragged my Downloads directory into the sidebar (it should be there already). So: command-tab to finder, click Downloads in the sidebar and viola. Alternatively, you could drag the downloads folder to the dock (it should be there already). Or, swipe 4 fingers down to reveal desktop (an option in system preferences -> trackpad), then click desktop to select finder.
In Automator you could build a workflow and save it as a service. In Automator use open finder and save as a service. This will put it in your Library to be available across applications. Then enable a quick key assigning a keyboard shortcut in system preferences -> keyboard -> keyboard shortcuts -> services.