Most likely, in an interview this question will sound like this: have you heard anything about Suspense. It is also often asked in the context of a conversation about optimization, and in particular React.lazy(). If you weren't asked about it directly, it's good form to logically complement lazy() with a mention of Suspense.
So, what is it?
Suspense is a mechanism for managing waiting. It lets you show a fallback UI while part of the application is not yet ready to render. Put simply, it is responsible for the content that is shown while React waits for something asynchronous. This can be a loader, a skeleton, or any other temporary content.
The main goal is to let the user know that the UI they need will appear in a few seconds. This way, the user doesn't get frustrated on a poor internet connection, which in turn has a positive effect on UX.
Let's look at a basic example of Suspense together with React.lazy().
In this example, we use lazy loading to wrap the Profile component, telling React that it should be loaded asynchronously. This technique is called code splitting, and you can read about it here.
While the component is not ready yet, the user will see a skeleton. Once loading finishes, React will automatically replace it with the Profile component.