Here are some key points about ServiceNow Jelly:

1. Scripting Language: Jelly used its own scripting language that was XML-based. Developers could use XML tags and attributes to define how UI elements should be rendered and interacted with.

2. Server-Side Rendering: Jelly scripts were executed on the server side, and the resulting HTML was sent to the client’s web browser. This allowed for server-side processing of data and logic.

3. Customization: Jelly was often used for customizing forms, lists, and other UI components within ServiceNow. Developers could create custom UI elements, modify existing ones, and control their behavior.

4. Incorporating Server Data: Jelly allowed developers to incorporate server-side data into the UI. This data could come from various sources, including ServiceNow tables and business logic.

5. Client-Side Interaction: While Jelly itself focused on server-side rendering, it could work in conjunction with client-side scripting technologies to provide dynamic user experiences.

6. Deprecation: ServiceNow has deprecated Jelly in favor of more modern and flexible technologies. This shift has led to the adoption of AngularJS for client-side scripting and UI Pages/UI Macros for server-side customization.

7. Upgrade Considerations: Organizations using older versions of ServiceNow that rely on Jelly for UI customization may need to migrate their customizations to newer technologies when upgrading to more recent ServiceNow releases.

8. Documentation: While Jelly is no longer the recommended approach, historical documentation and resources related to Jelly scripting may still be available for reference.