"The number of bars and waves"
A longer quotation from your sources:
OpenType features include hanging or lining numerals; slashed, dotted and normal zeros; and alternative shapes for a number of lowercase letters. The look of text can be tuned to personal taste by varying the number of bars and waves.
OpenType fonts can have glyph substitution features that, when activated, change the appearance of various characters. Some of these features include small capitals, text figures, and swash letters, as well as “anything goes” style variants called Character Variants and Stylistic Sets. Activating these features requires OpenType-aware applications, such as recent versions of Microsoft Word and LibreOffice, and more sophisticated publishing and graphics software (outdated partial list).
In the case of Consolas, there are several Stylistic Sets within the font that change the shape of several letters:
Note that in SS04 the f and r add “bars” at their bases, while in SS05 and SS06 the f, i, j, l, and r add various types of “waviness”. I’m sure this is what the quotation is referring to.