The term 'on end' can be solved in two ways in a crossword puzzle. The first solution is 'UPRIGHT, ' which is a seven-letter word meaning to be in a vertical position, perpendicular to the ground. The second solution is 'ERECT, ' which is a five-letter word meaning to be in a vertical position, standing straight up. Both words refer to the same concept of being in a vertical position, but 'UPRIGHT' is more commonly used to describe a person's posture, while 'ERECT' is more commonly used to describe an object or structure.