In typography, the "look" of the typeset letters in relation to each other, which may or may not be geometrically accurate due to optical illusions caused by the proximity of various letter shapes. In good typeface design, spacing between lowercase letters is "built in."
Letters come on three basic shapes, oval (such as an "O"), inclined (such as a "V"), or vertical (such as an "I"). The combined appearance of the spacing between letters is called optical volume, which can vary depending upon the shape of the letters. For example, the space between two squares may look different than that between two circles, even though they may be quantitatively the same. On modern typesetting and page makeup devices and software, automatic and manual kerning options can solve the problem of optical volume.