# `semantic.unknown_name`

Name is not declared.

Area 1, [Project layout and modules](../topics/project-layout-and-modules.md); not declinable; the next step is usually the agent's.

```jadpo
type Pair = Object {
    first: Missing
}
```

```text
error: `Missing` isn't declared
 --> main.jadpo:2:12
  |
2 |     first: Missing
  |            ^^^^^^^ not declared
  reason: Nothing in this project or the standard library is called `Missing`.
  next: Declare `Missing`, or use an existing name (agent)
  rule: semantic.unknown_name
  help: https://jadpo.dev/docs/errors/semantic.unknown_name

check failed: 1 error, 1 file
```