# Core Concepts
This section defines the core concepts of MeiliSearch:
- Documents: Objects made up of key-value pairs.
- Indexes: Entities that contain documents and search-related settings.
- Relevancy: Rules that help you get more intuitive results. The human element of your search engine.
MeiliSearch is an asynchronous API. This means that, unlike a synchronous API, it doesn't wait for the call to be done as calls are placed in a queue for processing. For further information please read the advanced guide.