It is important to note that the term 'Hamon' is not synonymous with the term 'tempered edge'. This itself is a misnomer because many lay people use the term in reference to the hardened edge of the blade. In a metallurgical context the term 'temper' means to soften, and relates to a precise process in the manufacture of a blade. There have been several very enlightening discussions of this topic in the Mailing Lists.
Hamon literally means 'edge badge' and refers to the line of nie/nioi which delineates the yakiba or hardened portion along the sharp edge of the blade from the Ji-hada or blade surface behind the hardened portion. The actual edge of the blade is termed the ha.
ito/hoso = narrow chû/naka = medium hiro = wide Ko = small Ô = large
These qualifying terms are used in conjunction with the main terms below for greater precision in describing the appearance of the hamon.