# Coordinator

> A helper that fetches data for many entities at once, on a schedule, so a device or API is asked once instead of once per entity.

Source: https://contributors.home-assistant.io/glossary/coordinator/

- In code: `DataUpdateCoordinator`, `CoordinatorEntity`
- Also: data update coordinator, update coordinator

Entities that get their data from a coordinator update together, when it has new data. The coordinator also handles errors in one place: when fetching fails, its entities become [unavailable](https://contributors.home-assistant.io/glossary/unavailable/).

## Related terms

- [Polling](https://contributors.home-assistant.io/glossary/polling/): Asking a device or service for new data on an interval. The opposite is push, where the device sends updates when something changes.
- [Entity](https://contributors.home-assistant.io/glossary/entity/): One thing Home Assistant can show, measure, or control, like a light, a temperature sensor, or a switch. Every entity has a state.
- [Unavailable](https://contributors.home-assistant.io/glossary/unavailable/): A special state for an entity that Home Assistant can't reach right now. Its counterpart, unknown, means it can be reached but has no value yet.