Content Type Hub is a central location where you can manage and publish your content types through out the organization.
Ex: You can create Content Type Hub Web Application and create few Content Types. These content types you can use in any other Web Applications and Site Collections by subscribing to the Content Type Hub. If you want to modify the content type, you can modify at Content Type Hub only. You can’t do the at tenant sites. It is an advantage to maintain same fields in one content type through the organization.
Fore more information about the CTH (Content Type Hub) please refer the below web links.
Link 1 : Understanding the Content Type Hub
Link 3: Content Type Hub in Office 365
Link 4: YouTube video on CTH