There are two types of variables that can be defined in a role. There are role variables, loaded from roles/<role_name>/vars/main.yaml, and there are role defaults, loaded from roles/<role_name>/defaults/main.yaml. The difference between vars and defaults has to do with precedence order. Refer to Chapter 1, The System Architecture and Design of Ansible, for a detailed description of the order. Role defaults are the lowest order variables. Literally any other definition of a variable will take precedence over a role default. Role defaults can be thought of as placeholders for actual data, a reference of what variables a developer may be interested in defining with site-specific values. Role variables, on the other hand, have a higher order of precedence. Role variables can be overridden, but generally they are used when the same dataset is referenced more than once within a role. If the dataset is to be redefined with site-local values, then the variable should be listed in the role defaults rather than the role variables.