Default: (if (eq (delivery-value :dll-exports) :no) :exe :dll)
image-type defines whether the image is to be an executable or a dynamic library, , just as for save-image.
The value can be :exe, :dll or :bundle. It defaults to :exe or :dll according to the value of dll-exports and therefore you do not normally need to supply image-type.
image-type :bundle is used only when saving a dynamic library. On Mac OS X it generates an object of type "Mach-O bundle" and is used for creating shared libraries that will be used by applications that cannot load dylibs (FileMaker for example). It also does not force the filename extension to be dylib. On other Unix-like systems image-type merely has the effect of not forcing the filename extension of the delivered image, and the format of the delivered image is the same as the default. On Microsoft Windows image-type :bundle is ignored.
On non-Windows platforms, image-type :bundle requires that the build machine has a C compiler installed. This is typically gcc (available by installing Xcode on the Macintosh).
Note:
image-type :bundle is completely unrelated to the Mac OS X notion of an application bundle.
LispWorks Delivery User Guide - 10 Aug 2017