An IAM user is a single person or service entity/application that interacts with AWS resources through service requests and modifications. AWS users consist of a name, password, and a pair of unique API access keys that grant them permissions according to policy condition criteria established by an administrator.
Roles are designed so that a set of permissions can easily be delegated to users on an individual basis. For example, instead of assigning an individual all their necessary permissions one at a time, they can be assigned a specific role that contains all the necessary permissions in a single step.
The difference between an IAM role and a user is that a role can be temporarily or permanently applied to a user to give the user bulk permissions for a task. Unlike a user, a role does not have associated passwords or credentials and can be easily applied to multiple users to grant access to a set of permissions at once.