A role definition is a collection of permissions that can be performed, such as read, write, and delete. It's typically just called a role. Azure role-based access control (Azure RBAC) has over 120 built-in roles or you can create your own custom roles.
There are 3 types of roles in Microsoft Azure:
The Web Role in a cloud application is a role supported by IIS7 and ASP.NET. It is used to provide a web-based front-end for your hosted service. This can contain websites or other code supported by IIS.
The Worker Role is used for generalized operations of the service. These are like worker bee. Worker roles may also perform background tasks for the web role. The worker role is ideal for long-running or intermittent tasks. Examples of tasks performed include: CPU intensive computations.
The VM or Virtual Machine Role is a special role that job is to define the configuration and updating of the operating system for the virtual machine. Both the web role and worker role run inside the VM role. It gives full control of operations.