What is an IAM role,and how it resolves connectivity b/w different AWS resources?

IAM role, are the ones via which an AWS resource gain access to other AWS services. Suppose an EC2 instance has to access files from S3 bucket so it cannot do it directly, as it lacks access privileges to connect with S3 resource. Hence, this EC2 instance is assigned an IAM role via let’s say - “S3 Admin” via which it gains access to S3 bucket. Also, the same can be applied to API calls where everytime credentials need not be supplied instead an IAM role is applied.