There are several terms that are regularly used when discussing font faces that may not be commonly understood by the layperson. This introduction to my typography blog will cover the definitions of some of those basic terms. The definitions I'm using here are found in Typographic Design: Form and Communication, 5th edition. However, these are terms that date back to the beginning of of printing and moveable type and similar definitions can be found elsewhere.
Describing Letters
Baseline: The imaginary that the base of each capital sits.
Capline: The imaginary line that runs along the top of the capital letters.
Meanline: The imaginary line that establishes the height of the body of lowercase letters. This is often the 'mean' between the Capline and Baseline.
Beard line: The imaginary line that runs along the bottom of the descenders.
x-height: The distance from the Baseline to the Meanline. This is typically the height of lowercase letters (most easily measured on the lowercase 'x').
Optics: All characters align optically on the Baseline. The body height of lowercase characters align optically at the x-height and the tops of the capitals align at the top of the Capline.
Ascender: A stroke on a lowercase letter that rises above the Meanline.
Descender: A stroke on a lowercase letter that falls below the Baseline.
Serif: The short strokes that extend from and at an angle on the upper and lower ends of the major strokes of a letterform.
Sans-Serif: Describes a letterform without Serifs.
Stroke: Any of the linear elements within a letterform.
There are additional terms describing the nuances of type (Bowl Counter, Ear, Eye, Hairline, Leg, Spur, Stem, Tail...) that I may further cover in later posts if the need arises, when discussing specific fontfaces.
Weight: The ratio between the relative width of the strokes of a letterform and its height. This is described as Bold or Light.
Width: The ratio between the black vertical strokes and the intervals of white (i.e., whitespace or negative space - the enclosed area - bowl, loop or eye). This is described as Expanded or Condensed.
Thick/Thin Contrast: The visual relationship between a letters thickest and thinnest parts.
Stress: The visual axis of a letter.
Letterspacing
Leading: (pronounced LED-ing) The vertical space between lines of text. The name comes from original typesetters would add pieces of lead between lines of type to create more space. Non-designers are most familiar with this concept from the program Microsoft Word where it is simplified as 'single' or 'double-spaced'. In this example, the term 'double-spaced' would mean that if you are using a 12 point font there would be a (approximately) 24 point space between lines. More Leading (in the 'double-space' example) makes each line of text easier to read. Most books read for leisure would have more leading.
Tracking: Tracking is the consistant horizontal spacing between characters. Smaller type tends to need a wider Tracking, while Larger type like headers or titles can have a tighter Tracking.
Kerning: The horizontal spacing between individual characters. This is different between Tracking because it deals specifically with pair of characters. You may apply Tracking to a block of text, but you would apply Kerning to individual letter pairs to adjust them if they look spaced visually incorrect.
Sources
Carter, Rob, Philip B. Meggs, and Ben Day. Typographic design: form and communication. 3rd ed. New York: John Wiley & Sons, 2002. Print.
Dodd, Robin. From Gutenberg to opentype: an illustrated history of type from the earliest letterforms to the latest digital fonts. Vancouver: Hartley & Marks, 2006. Print.
Type samples image used without permission, from Typographic Design: Form and Communication, 5th ed., Carter/Day/Meggs
