Citation:
Reversing a string means to change the order of its characters, so that the last character becomes the first, the second-to-last becomes the second, and so on.
A substring is a smaller part of a larger string. It can be obtained by extracting characters from within the original string.
The length of a string refers to the number of characters it contains.
Concatenation: Concatenation is combining two or more strings together to create a new string.