What is bad typography?

Bad typography covers a wide range of mistakes people make when setting type in a document. Too short line length in relation to type size, not enough or too much leading, too many hyphens, generally anything that is hard to read. Also, over use of all caps, underline and bold, false italics and too many typefaces, A person who sets type needs to know about ligatures, em and en dashes, true quotation marks, and be familiar with a wide variety of typefaces. One example of bad typography is the use of a font like Comic Sans for a professional notice or a serious subject.