Arrays are fixed-length containers, containing N elements where each element is of the same size. They are stored in contiguous/uninterrupted segments of free memory which means that all of the elements are adjacent - lined up next to each other in memory. Just like every slot in the memory gets associated with a number, each element of an array gets associated with a number from the range [0, N-1]. This number is called an index & the process of assigning this number to each element is called indexing.