Citing implementation about them:
With an array, you can use the array index to access any element immediately. This is called random access.
Whereas,
With a linked list, you have to start at the top of the list and then move from node to node until you get to the node you want, which is termed sequential access.
References:
LinkedList Vs Array
Random_Access
Additional read:
java.util.RandomAccess is marker class that is used to indicate that they(Collections) support fast (generally constant time) random access.