This is the most valuable type of reuse, where a whole architecture, not just a piece of code, is reused.

The software architecture includes the structure of the system/subsystem, and consists of software (and/or hardware) components, and the relationships between them.

Just as there are constraints to writing reuseable pieces of code, there are constraints on architectures to ensure that they are reusable.

These constraints pertain not only to the basic functionality of the system, but also to its style, form, and the nature of the components that it uses.