Last updated at 5:22 am UTC on 23 May 2017
The Squeak image is a file which is an exact copy of the Squeak memory content with all class definitions and objects.
(Is this definiton correct? Almost. Objects that depend on operating system resources may tweak their image saving/loading. For example, a network socket definitely won't exist when you reload an image, so mumble mumble happens.)
This image of objects runs on top of a Virtual Machine. The image is a platform-independent file. In other words, the exact same image file can run on a Windows/Mac/Unix/etc platform, as long as the appropriate virtual machine for the platform is used.
The image does not contain the source code for the system, however. The source code is stored in the .sources file and the .changes file.