What is the meaning of Word_ladder?

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.

A type of cryptic crossword clue in which the each word in the clue defines a single term each varying by a single letter, and all the terms together form a word ladder between the first half of the solution and the second half.

Source: wiktionary.org