DjangoProject là toàn bộ website — 1 settings, 1 deployment. App là một module nghiệp vụ nằm trong project, đóng gói riêng models.py, views.py, urls.py, migrations/, có thể bê đi cài lại ở project khác. Một project chứa nhiều app.
Ví dụ một shop: project mystore chứa các app accounts (user/profile), catalog (product/category), orders (cart/checkout), payments (gateway). Mỗi app gói trọn một mảng nghiệp vụ — đó chính là ý "reusable app" mà Django nhắc tới.
Project is the whole website (one settings, one deployment); app is a reusable business module inside that project. A project contains multiple apps, each with its own models.py, views.py, urls.py, migrations/.
A shop example: project mystore holds apps accounts (user/profile), catalog (product/category), orders (cart/checkout), payments (gateway). Each app can be packaged and installed in another project — that is what "reusable app" means.
How to split: along bounded contexts of the business. Do not jam everything into one huge core app — touching one thing drags migrations for 30 models. Also do not over-split (one app per model) — overhead with no real reuse.