To get started with TanStack Query, you need to understand several key terms that form the backbone of how it operates in your React applications. A query is a request for data, typically from a server, that TanStack Query tracks and manages. You use queries to fetch data and keep it in sync with your UI. In contrast, a mutation is an operation that modifies or writes data on the server, such as creating, updating, or deleting a record.

TanStack Query uses a cache to store the results of queries. This cache ensures that data is readily available without unnecessary network requests, improving performance and reducing loading times. When you change data on the server, you may need to invalidate certain queries. Invalidation tells TanStack Query that cached data is no longer fresh and should be refetched.

The stale time is the period during which cached data is considered fresh. After this time passes, the data becomes stale, and TanStack Query may fetch new data when needed. Background refetching refers to TanStack Query's ability to automatically fetch updated data in the background, so your UI can display the latest information without manual intervention.

To visualize how these concepts work together, imagine the flow of data in a TanStack Query-powered app. When your component mounts, a query fetches data and stores it in the cache. If you trigger a mutation, such as updating a user's profile, the cache for the relevant query is invalidated. TanStack Query then automatically refetches the data, ensuring your UI shows the most up-to-date information. The system manages when data is considered fresh or stale, and can refresh data in the background as needed.

[Component Mounts]
        |
        v
 [Query Fetches Data]
        |
        v
 [Cache Stores Data]<----------------------------.
        |                                        |
        v                                        |
[Data Displayed in UI]                           |
        |                                        |
        v                                        |
   [Mutation Occurs]    (User updates data)      |
        |                                        |
        v                                        |
[Invalidate Cache for Query]                     |
        |                                        |
        v                                        |
   [Background Refetch]--------------------------|
        |
        v
[UI Receives Updated Data]

To make these ideas more relatable, think of queries and mutations like a library. A query is like checking out a book: you ask the librarian (server) for a book (data), and they give you a copy to read (cache). As long as you keep the book, you don't need to ask for it again unless it's out of date (stale). A mutation is like returning a book with a note to update its content. The librarian updates the book, and the next person who checks it out gets the latest version. The system keeps track of when books need to be updated (invalidation and background refetching), so everyone always has access to the most current information.