by default the Mac does a pretty good job of hiding system folders from users. They don't show up in the Finder, and when you search in Spotlight they don't include results from those folders. But if you're a developer, this can be a bad thing. There are times when it'd be really nice to search in /etc or /var using Spotlight. Yeah, you can use the find command in the Terminal window, but Spotlight is just a lot nicer to user.

If you want to search a system folder in Spotlight, here are the steps that make this happen:

1) Open a Finder window.

2) From the menu bar, select Go -> Go to Folder... and enter the name of the folder you want to select.

3) Go up to the search widget in the Finder and enter your search term.

4) By default, the search will take place in This Mac (near the the top of the window). But you can click the name of your current folder which should be right next to it.

Once you do this, Spotlight will search in your folder, and this can include any folder on your drive. Witness the result: