Keys help React identify which items have changed, are added, or are removed. Keys should be given to the elements inside the array to give the elements a stable identity. The best way to pick a key is to use a string that uniquely identifies a list item among its siblings.
The 'key' prop is used to assign a unique identity to each element in a list of elements. React uses the 'key' prop to efficiently update and re-render components in a list when the underlying data changes.
It helps React identify which items were added, removed, or re-ordered, leading to better performance and fewer re-renders.
Most often you would use IDs from your data as keys. When you don't have stable IDs for rendered items, you may use the item index as a key as a last resort. It is not recommend to use indexes for keys if the items can reorder, as that would be slow.