Final answer:
Omitting the last index in a slice operation returns elements from the starting index to the end of the list or array.
Step-by-step explanation:
When indexing a list or array in many programming languages, if you omit the last index (after the colon), the slice returned will start at the index specified before the colon and continue to the end of the list or array.
For example, in Python, my_list[2:] would return all elements from the third element (since indexing starts at 0) to the last element in my_list. This is because the slice syntax defaults to the end of the array when the ending index is not specified.