A wiki template is not really what you would call a "template" in real world. In a wiki, we usually call that a "boilerplate".
What is a Template?
A wiki template is an article, just like any other, but with the ability to be embedded into other pages which can be used anywhere in the wiki.
If you have made a table that you would like to include in more than one place and the data may change you can create a template for it. An example of this would be Template:Druid_Class which contains details of the Druid class. This is used on a number of different pages. The template was created and the template code {{Druid_Class}} simply added to the place where the Druid box will appear.
If and when any details change only the one template needs to be updated and the changes will appear on all the pages where that template is called.
All Templates
This is the list of all templates.