An index route can be thought of as a default child route. In React Router, if no children match a parent route, it will display an index route if one is defined. An index route has no path and instead has a index boolean property:
const router = createBrowserRouter([
{
path: '/',
element: <App />,
errorElement: <ErrorPage />,
children: [
{index: true, element: <HomePage />},
{path: 'products', element: <ProductsPage />},
{path: 'products/:id', element: <ProductPage />}
]
},
]);