# Application programming interface (API)

A defined way for software systems to request data or actions from one another.

A defined way for software systems to request data or actions from one another.

## An example

A publisher sends an ad request to an API and receives an eligible offer.

## Why it matters

An API contract needs clear inputs, responses, authentication and failure behavior.


## Related terms
- [Ad placement](https://jolts.xyz/resources/glossary/ad-placement)
- [Ad spend](https://jolts.xyz/resources/glossary/ad-spend)
- [Advertiser](https://jolts.xyz/resources/glossary/advertiser)
- [Publisher](https://jolts.xyz/resources/glossary/publisher)

## Next step

[Explore advertising](https://jolts.xyz/advertisers) or [monetize your AI app](https://jolts.xyz/publishers).