> ## Documentation Index
> Fetch the complete documentation index at: https://docs.outerlayer.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Key concepts

> The words every other page uses, each defined once.

Everything in OuterLayer hangs off a **work item**. An issue becomes a work item when it is added to a factory's Work page. Sessions, pull requests, checks and reviews all attach to the item, not to each other.

```mermaid theme={"system"}
flowchart LR
    I["Issue<br/>owner/repo#42"] --> W["Work item #7"] --> M["Shipped<br/>cost · time · pass or fail"]
    S["Sessions"] --- W
    P["Pull requests"] --- W
    C["Checks"] --- W
    R["Reviews"] --- W
```

Because checks attach to the item, a check still counts when one pull request is closed and another opens in its place.

## Where work lives

| Term | What it is |
| - | - |
| Organization | Your company's account. It holds members, roles and billing, and one or more factories. |
| Factory | One team's unit of work: its Work page, repositories, keys and policy. `appId` in config files and the API is the factory's id. |
| Work page | The factory's list of work items. |
| Work item | An issue added to the Work page. It gets a number of its own on the factory: issue 42 might be item 7. Commands and `OUTERLAYER_WORK` take the item number, never the issue number. |
| Item page | One work item's page. Its tabs are **Activity**, **Criteria**, **Findings** and **Checks**, with the item's sessions and pull requests beside them. See [Review and merge](/review-the-work#the-item-page-is-the-review). |
| Context source | One repository that supplies agent instructions and policy to the factory's other repositories. CLI commands and messages call it the **control plane**. See [Share instructions across repositories](/share-instructions-across-repositories). |

## Who does the work

| Term | What it is |
| - | - |
| Session | One run of a coding agent. It uploads only when it was started with `OUTERLAYER_WORK` set to an item number. See [Launch a session](/launch-a-session). |
| Build | One attempt to turn an item into a pull request, either on a host or in a session you start yourself. |
| Host | A machine running `outerlayer runner` for the factory. It takes the items queued with **Build**. See [Run work on your machines](/run-work-on-your-machines). |
| Runner | The `outerlayer runner` process on a host. |
| Claim | The hold a host, or a person's session, has on an item while it works on it. While it lasts, no host starts the item. It expires unless it is renewed, so a stopped machine never holds an item for long. |
| Lease | The name error codes, flags and the CLI use for a claim. A session's lease lasts 20 minutes, and its hooks renew it while the session works. A host renews its own while the build runs. |
| Item key | The key a host's build uses in place of the runner's key. It acts only on the claimed item and stops working when the claim ends. See [Item key](/reference/cli-runner#item-key). |
| Pull request | Joins an item when a session on that item declares it. See [Declare a pull request](/declare-a-pull-request). |

## How the work is judged

| Term | What it is |
| - | - |
| Policy | `.outerlayer/policy.yaml`, read from each pull request's base branch. It says which checks run and whether a failing one blocks the merge. See [Policy and validators](/policy-and-validators). |
| Validator | A file in `.outerlayer/validators/` that declares one check: its name, the sentence it shows, and what satisfies it. |
| Check | One named pass or fail on the item, such as "a code review report is attached". A check holds across every pull request the item has. The item page's **Checks** tab lists them. |
| Evidence rows | The item's checks, one row each. They show on the item page's **Checks** tab. When **Post session summaries on pull requests** is on, they also appear in the **evidence comment** on each pull request. |
| Acceptance criteria | The list of what the item must do. The item page's **Criteria** tab shows the list recorded with [`outerlayer emit criteria`](/reference/cli-emit#outerlayer-emit-criteria). A criterion missing its declared proof flags the verdict. |
| Artifact | A file attached as proof. Its file type sets its kind: a screenshot, a video, a report, a log, a test result, or a plain file. See [Attach evidence](/attach-evidence). |
| Review | A person's pass or fail on the whole item. A review is not a check. Only a person records one, on the item page or with `outerlayer work comment --pass` or `--fail`. See [Review and merge](/review-the-work). |
| Finding | A problem an agent hit in the factory while it worked, such as a flaky test or a wrong instruction. Findings never affect whether the work passes. |

## Where an item stands

Every item has one status that says whose turn it is, from **Not started** to **Done**. The list of statuses and what each means is on [Review and merge](/review-the-work#the-item-page-is-the-review).


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