Lists (also known as the array abstract data type) are often implemented by the array data structure.
The items in an array can be anything from primitive types such as integers to more complex types like instances of classes.
For a Array (data structure), the size is fixed and cannot add more values than it's size unless the array is resized or something is taken out.
Each "slot" in the array has an associated number, called an index. By using these numbers, the programmer can directly index into the array to get specific values, which makes them very efficient.