What does "three across" mean?

Answer 1

It's the name of a crossword clue. Clues for crossword puzzles are sorted into two lists, named "Across" and "Down", for the direction the word goes in the puzzle. The clues in each list are numbered so you will know where to put the word in the puzzle. So "three across" is the name of the word or clue that goes with the horizontal space labeled 3.