README: Define terminology as a base for internal refactoring

README.md

@@ -22,3 +22,36 @@ or using a browser: `http://localhost:9090`
 
 Please refer to the [lorax-composer](https://github.com/weldr/lorax)'s documenation as osbuild-composer is a drop-in replacement.
 
+## High-level overview
+
+![overview](docs/osbuild-composer.svg)
+
+### Frontends
+
+`osbuild-composer` is meant to be used with 2 different front-ends. The primary one, which is meant for general use, is cockpit-composer. It is part of the Cockpit project and unless you have a strong reason not to use it, you should use it. `composer-cli` is a command line tool that can be used with `osbuild-composer`.
+
+### Compose
+* Compose is what the user submits over one of the frontends
+* It contains of one or more **image builds**
+* It contains zero or more **upload actions**
+
+### Image build
+* The resulting *image* has a *type*: https://github.com/osbuild/osbuild-composer/blob/master/internal/distro/fedora30/distro.go#L19
+* Running build in osbuild-composer is referred to as a "job" (internal terminology, not related to end-user experience)
+
+### Job
+* What composer submits to a worker
+* Is a unit of work performed by `osbuild` (internally it is a single execution of `osbuild`)
+* Consists of **one** image build and **zero or more** Upload actions
+
+### Image type
+* In the cockpit-composer, for examples these are image types:
+  * Openstack
+  * Azure
+  * AWS
+* As of now, we name them internally by their file format: vhd, ami, etc.
+* You can see a list of types by executing: `composer-cli compose types`
+
+### Upload action
+* Each image can be, but does not have to be, uploaded to a remote location
+* One image can be uploaded to multiple locations