What does the final if statement mean in the program.

8.5 def rotate(letter.n): if letter.islower): start-ord(a') else:return letter l-ord(letter)-start c=(1+n)%26 +start return chr(c) def rotateword(word,n): res = " for letter in word: res+=rotate(letter,n) return res if name =-' main print rotateword('cheer',7)) print(rotateword('melon',-10)) print(rotateword(sleep',9))