A location on a horizontal line that marks the beginning of a column of text. With a monospaced font such as Courier, space characters can be used to line up columns of numbers and names evenly. However, when a proportional font is used such as Arial or Times Roman, the varying widths of letters require the use of preset tab stops for proper alignment. With typewriters, tab stops are mechanical elements that halt the movement of the carriage. In word processing, they are numerical settings maintained by software. See tab.