Often a Lisp program at runtime consist of a 'runtime environment' (memory management, ...) and the data in the heap: functions and all kinds of Lisp objects (characters, lists, hash tables, CLOS objects, ...). An 'image' is a saved dump of this memory.<p>Typically you can start Lisp and just reload the memory from the heap dump (the image) on disk and do some automatic re-initialisations (for example reopen windows, reconnect to files and databases, restart processes, ...). All the code and data will be restored. You are back, where you saved the image before.<p>Imagine you would dump the memory of your JVM to disk and restart it later.<p>The Lisp vendor will provide you with an 'image' that contains the base language, some extensions, graphics, networking, editor, debugger, inspector, gui designer, etc.. You can then write a program, load all the program files, load all the data and configuration files and save an image. When you restart the image later, all your application code and data is back. This can save a lot of time during development.