A bar or stroke is a modification consisting of a line drawn through a grapheme. It may be used as a diacritic to derive new letters from old ones, or simply as an addition to make a grapheme more distinct from others. It can take the form of a vertical bar, slash, or crossbar.
A stroke is sometimes drawn through the numerals 7 (horizontal overbar) and 0 (overstruck foreslash), to make them more distinguishable from the number 1 and the letter O, respectively.
For the specific usages of various letters with bars and strokes, see their individual articles.