What is a tag? - Amazon EMR
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What is a tag?

A tag is a label that you assign to an Amazon resource. Each tag consists of a key and a value, both of which you define. Tags enable you to categorize your Amazon resources by attributes such as purpose, owner, and environment. When you have many resources of the same type, you can quickly identify a specific resource based on the tags you've assigned to it. For example, you can define a set of tags for your Amazon EMR Serverless applications to help you track each application's owner and stack level. We recommend that you devise a consistent set of tag keys for each resource type.

Tags are not automatically assigned to your resources. After you add a tag to a resource, you can modify a tag’s value or remove the tag from the resource at any time. Tags do not have any semantic meaning to Amazon EMR Serverless and are interpreted strictly as strings of characters. If you add a tag that has the same key as an existing tag on that resource, the new value overwrites the earlier value.

If you use IAM, you can control which users in your Amazon account have permission to manage tags. For tag-based access control policy examples, see Policies for tag-based access control.