What is the difference between a tap and a click? I can click on both my Magic Trackpad and my Magic Mouse but I can tap on neither, if my understanding is correct. 

On my Magic Mouse all I can do is click. Same with Magic Trackpad.

What am I missing? I have searched web but it is hard to get relevant answers.
I am using a mid 2011 iMac with 10.11 beta but this has bothered me since Lion.
I have enabled Tap to click, but the situation is the same and my basic question is what is the difference? 

Edit 2

After several reboots the trackpad now responds to tap, mouse does not.
According to this article: Turning On Mac Touch-To-Click Support from the Command Line you have to enable the feature in the command line:

Enable the general tap-to-click behavior:

sudo defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad Clicking -bool true


Enables tap-to-click for the Magic Mouse:

sudo defaults -currentHost write NSGlobalDomain com.apple.mouse.tapBehavior -int 1


Enable tap-to-click at the login and boot screens of OS X:

sudo defaults write NSGlobalDomain com.apple.mouse.tapBehavior -int 1


and reboot your Mac.

To disable all this enter in Terminal:

sudo defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad Clicking -bool false
sudo defaults -currentHost write NSGlobalDomain com.apple.mouse.tapBehavior -int 0
sudo defaults write NSGlobalDomain com.apple.mouse.tapBehavior -int 0


and reboot again.