# Concepts and definitions
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This section describes key concepts and defines terminology specific to this solution:

 **origin** 

The source location where original images are stored, which can be an Amazon S3 bucket or an external HTTP-accessible domain.

 **transformation policy** 

A reusable configuration that defines a set of image transformations, output settings, and conditional logic that can be applied to image requests.

 **mapping** 

Configuration that routes image requests to specific origins based on request path patterns or host headers.

 **cross-origin resource sharing (CORS)** 

Defines a way for client web applications that are loaded in one domain to interact with resources in a different domain.

 **fallback image** 

Image that you set to show when the intended image doesn’t load.

**Note**  
For a general reference of AWS terms, see the [AWS Glossary](https://docs.aws.amazon.com/general/latest/gr/glos-chap.html).