Oracle Fusion Applications is a suite of business applications designed to work together to improve business performance and adapt to changing business requirements. It covers a wide range of functional areas, including finance, human resources, supply chain management, customer relationship management, and more.

When it comes to development and extensibility in the context of Oracle Fusion Applications, developers can extend and customize these applications to meet specific business needs. This can involve:

1. Customizations: Tailoring existing Fusion Applications modules to fit the unique processes and requirements of a business.

2. Extensions: Developing new features, modules, or components that integrate seamlessly with the existing Fusion Applications suite.

3. Integrations: Integrating Fusion Applications with other software systems, databases, or external services.

4. User Interface Customization: Modifying the user interface to provide a more intuitive and personalized experience for users.

5. Reports and Analytics: Creating custom reports, dashboards, and analytical tools to gain insights from the data within Fusion Applications.

6. Data Migration and Conversion: Managing the migration of data from legacy systems to Fusion Applications.