OS X Terminal: Activate focus follow

By default, mouse focus for Terminal is determined by clicking on the desired window, but it is often more convenient to have the focus automatically follow the mouse to any Terminal window.

defaults write com.apple.terminal FocusFollowsMouse -string true

To make the command take effect, you need to restart Terminal.

Revert to the default setting, change boolean in false

defaults write com.apple.terminal FocusFollowsMouse -string false