> ## Documentation Index > Fetch the complete documentation index at: https://docs.gradial.com/llms.txt > Use this file to discover all available pages before exploring further. # Core Concepts > The terms that define authoring, approval, personalization, and delivery in Gradial ACI. These concepts form the working model for Gradial ACI. The most important distinction is between work in progress, approved work, content selected for publication, and the release currently serving visitors. ## Content and frontend concepts | Concept | Meaning | | - | - | | **Page** | A route-backed content document composed from a layout and ordered component blocks | | **Fragment** | Reusable content referenced by one or more pages or layouts | | **Component contract** | A typed definition of the props and asset slots a component accepts | | **Layout contract** | A typed definition of a page layout, including its regions, slots, and defaults | | **Registry** | The project mapping that pairs contracts with their Astro or React runtime components | | **Overlay** | A targeted change applied over base content for a dimension such as locale or audience | | **Code build** | A versioned build of the frontend that can be linked to a branch and used for preview or release | Content contracts stay framework-neutral. Runtime components own framework imports, styling, and rendering behavior. ## Versioning and approval concepts | Concept | Meaning | | - | - | | **Version** | An immutable saved state in ACI's content history | | **Branch** | An isolated line of work with its own content versions | | **`main`** | The approved content trunk. Landing a branch here records approval but does not make the content live | | **Land** | Apply an approved branch's changes to `main` after conflicts and validation are resolved | | **`live`** | The content trunk selected for the next site release | | **Promote** | Move selected paths from `main` to `live` | | **Drift** | The approved content in `main` that has not yet been promoted to `live` | A branch is not a version, and `main` is not the live website. Those distinctions make it possible to review a series of changes together, approve them, and still control when individual paths become public. ## Compilation and delivery concepts | Concept | Meaning | | - | - | | **Compilation** | Validation and preparation of content against a specific code build | | **Release** | An immutable, deployable set of site artifacts produced from `live` content and a code build | | **Stage** | Prepare a release alongside the release currently serving traffic | | **Activate** | Make a staged release current | | **Release rollback** | Return traffic to a previously staged release as a whole | | **Preview** | A branch-specific rendering of saved content with that branch's linked code build | A content rollback and a release rollback solve different problems. To restore an individual path, select the intended earlier content version and publish a new release. To restore the entire site state, roll back the active release. ## Personalization concepts | Concept | Meaning | | - | - | | **Base experience** | The default content served when no personalization applies | | **Segment** | Membership criteria evaluated from allowed visitor signals | | **Audience** | A targetable group used to select an experience | | **Experience** | The content a visitor should receive for an audience or experiment arm | | **Variant** | A compiled release artifact produced from a base experience plus its applicable overlay | | **Experiment arm** | One of the experiences compared within an experiment | ACI evaluates audience eligibility at request time, but it does not build personalized content at request time. Base and variant artifacts are prepared during release compilation. Unknown, unconsented, or unmatched visitors receive the base experience. ## Three boundaries to remember They have separate histories and are paired deliberately for preview and release. Landing moves work to `main`; promotion selects content for `live`; activation changes the site visitors receive. ACI determines an eligible variant at the edge, then serves or renders that exact compiled artifact. *** *Next: [Developer Quickstart →](/aci/developers/quickstart)* This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.