Amazon Machine Image (AMI)
So, when you want to launch an EC2 instance, you need an operating system, few pre-installed software packages, memory and types of storage, etc. All these information is provided by Amazon Machine Image (AMI).
AMI is defined as the information required to launch an EC2 instance in the cloud. This AMI forms a template for root volume of an instance. It controls the launch permissions and also takes care of storage mapping. They form the skeleton structure of an instance.
Any number of instances can be launched from a single AMI.
You can create your own AMI or use the existing AMI's created by AWS community or buy from AWS marketplace depending on the need.
The number of AMIs available differ from region to region in AWS.