The templates in Nagios allow you to create a set of parameters that can then be used in the definitions of multiple hosts, services, and contacts. The main purpose of the templates is to keep parameters that are generic to all objects, or a group of objects, in one place. This way, you can avoid putting the same directives in hundreds of objects, and your configuration is more maintainable.
Note
Nagios allows an object to inherit from single or multiple templates. The templates can also inherit from other templates. This allows the creation of very simple templates, where objects inherit from a single template as well as complex templating system, where actual objects (such as services or hosts) inherit from multiple templates. It is recommended to start with a simple template. Multiple templates are more useful when monitoring larger number of hosts and services across multiple sites.
It is also good to start using templates for hosts and services, and decide how they...