Amazon CloudFront is a content delivery network (CDN) offered by AWS. Content delivery networks provide a globally-distributed network of proxy servers which cache content, such as as .html, .css, .php, web videos and image files, to users, more locally to consumers, thus improving access speed for downloading the content. CloudFront can be used to deliver static, dynamic, streaming and interactive content. CloudFront operates on a pay-as-you-go basis. CloudFront competitors include larger content delivery networks such as Akamai and Limelight Networks.
CloudFront delivers your content through a worldwide network of data centers called edge locations. Edge locations are places where data will be cached and is different from regions or availability zones. When a user requests content, the user is routed to the nearest edge location ( edge location with lowest latency). If the content is already there in that edge location, CloudFront delivers it immediately; else, CloudFront retrieves it from a specified source such as an Amazon S3 bucket or an HTTP server and cache it.
Imp Note: Edge locations are not just read only, but you can write (PUT) to them too; this object will be put to the original location as well.
Distributions and Origins
CloudFront distributions specify the origin for files that CloudFront CDN will distribute. Distributions can be web distributions (to download content using the HTTP or HTTPS protocols) or RTMP distributions (for media streaming). A distribution has a unique CloudFront.net domain name (e.g. abc123.cloudfront.net). You can also map your own domain name to a distribution.
Origin for a cloudfront CDN distribution can be an S3 bucket, an EC2 instance, an elastic load balancer or Route53. Though CloudFront is optimized to work with AWS origins such as S3, EC2, Elastic Load Balancer and Route53, it can work well with non-AWS origin servers too that stores the original definitive versions of your files.
Imp Note: Objects are cached according to the TTL. You can clear the cached objects before the TTL, but will be charged.
Read more @ reference links.
CloudFront FAQ: https://aws.amazon.com/cloudfront/faqs/