A DocType will always belong to a module, to enable easier grouping of related models. Frappe comes with a lot of built-in modules. For e.g

  1. Core - contains doctypes like DocType, DocField, Report, System Settings, etc
  2. Desk - contains doctypes like ToDo, Event, Note, Kanban Board, etc
  3. Email - contains doctypes like Email Account, Newsletter, Email Group, etc

Modules also helps in grouping of code files in directories. The controller files generated by a DocType will live in it's respective Module directory.

frappe
├── commands
├── config
├── core
│   ├── doctype
│   │   ├── doctype
│   │   ├── docfield
│   │   ├── report
│   │   ├── system_settings
│   │   ├── ...
│   │   └── ...
│   ├── page
│   ├── report
│   └── web_form
├── desk
│   ├── doctype
│   │   ├── ...
│   │   ├── event
│   │   ├── kanban_board
│   │   ├── note
│   │   └── todo
│   ├── form
│   ├── page