In Odoo, ir stands for Information Repository. It is a prefix used for many models that handle Odoo's core data, configuration, and infrastructure. These ir_* models are essential for Odoo's framework and manage things like attachments, access rights, fields, actions, and more.

Here are some commonly used ir_* models and their purposes:

1. ir.attachment – Manages file attachments stored in the system (documents, reports, images, etc.).
2. ir.model – Stores metadata about models (database tables) in Odoo.
3. ir.model.fields – Defines the fields of each model (technical details of database columns).
4. ir.rule – Defines record rules for access control (restricts what records users can see).
5. ir.actions.* – Manages different types of actions, such as:
   • ir.actions.act_window: Defines window (form, list, etc.) actions.
   • ir.actions.report: Defines reports.
   • ir.actions.server: Defines server actions (Python scripts).
6. ir.config_parameter – Stores system-wide settings (key-value pairs for configurations).
7. ir.cron – Manages scheduled actions (cron jobs).
8. ir.sequence – Generates unique numbers for invoices, sales orders, etc.
9. ir.translation – Handles language translations.

These ir_* models form the backbone of Odoo's ORM (Object-Relational Mapping) and provide infrastructure for modules to extend and customize the system.

If you're working with custom development, understanding these models can help you manipulate Odoo's behavior efficiently.