An image refers to a Glance image.
An image is a collection of software resources that emulate an operating system environment on a physical computing device.
An image comprises a virtual operating system environment that can be ported from one physical computing device to another physical computing device.
It is possible to install user applications on an image just as you could on a physical computing device having an operating system installed on it.
Images with cloud-init packages
images with cloud-init are cloud ready, and such images offer the ability to automate typical server bootstrapping and configuration operations.
Images without cloud-init packages
Operating systems without cloud-init require the user to either manually perform configuration changes after VM creation, or automate these tasks utilizing a separate configuration management tool such as Puppet, Ansible, Salt, or Chef.