What is "word ladder"

n. A kind of puzzle in which one word must be transformed into another specified word of the same length by changing one letter at a time, each step yielding a valid intermediate word, as in ''lead → load → goad → gold''.

Word ladder (also known as Doublets, word-links, change-the-word puzzles, paragrams, laddergrams, or Word golf) is a word game invented by Lewis Carroll. A word ladder puzzle begins with two words, and to solve the puzzle one must findlink the two, in which two adjacent words (that is, words in successive steps) differ by one letter.