Refers to the thick-thin tendency of the strokes–an indication of typographic legacy

Stress, of course, can be good or bad. This sort is a good sort.

A word drawn in Uncial. This is highly-stressed, at about 45 degress, due to the slant of the pen-tip used to draw it. (courtesy [1] Wikipedia)

When speaking typographically, of course, stress essentially means how the strokes in the individual glyph goes from thick to thin. Conventional wisdom holds that the thick-thin transitions in many well-known typefaces come from thier origins in the brush-stroke writings of calligraphers who operated before type became movable.

A good example can be found in a script called Uncial, a handy example of which can be seen in the illustration. This script was written with a pen with a wide-edge held at about a 45-degree angle. This is a highly-stressed example; if one drew a line through the thinnest parts of the counter of the minuscule “a” (or a notional “o” written with the same nib) one may indeed find that this line is about 45-degrees from the vertical. This is also termed a stress of 45 degrees.

Knowing where stress comes from we can make judgements about the modernity of a given font’s heritage given what the stress of the glyphs are: fonts such as Garamond are thought of as “old style” because they have stress which suggests being drawn with a calligrapher’s pen; fonts such as Paul Renner’s Futura, with thier strokes of universal thickness, can be correctly regarded as quite modern (without respect to the rather obvious name).