A crossword puzzle is made up of three parts: the grid, the fill, and the cluing. The crossword grid is the arrangement of black-and-white squares you see when you open up your newspaper and turn to the puzzle page. The fill is the set of correct answers that, when you're done, will populate the puzzle; cluing is the list of prompts and hints, numberered sequentially across and down, that when interpreted correct will yield the fill. Yet another term to know is "keying" - which is the placement of letters so that they form a word, phrase, or abbreviation. A stand-alone letter would be completely unkeyed; a letter in a corner, where it becomes part of the 1-accross and 1-down word, would be double-keyed. In crosswords, a "word" is defined as any single answer across or down; quite comonly, a "word" in the puzzle sense is in fact made up of several real words.