Glossary Term Definition
A serif that flows naturally out of the main stroke through a continuous curve, as in humanist and Renaissance typefaces.
Definition
A reflexive serif is one that emerges from the main stroke through a smooth, continuous curve — as if the pen never left the surface. This organic transition between stroke and serif is characteristic of humanist and Renaissance typefaces, where the letterforms retain the logic of broad-nib calligraphy. Reflexive serifs contrast with transitive serifs, which join the main stroke at an abrupt angle. Jenson's roman and Griffo's types for Aldus are classic examples of reflexive serif construction.
Source
No access — Robert Bringhurst — p. 344:
A serif that flows smoothly out of the main stroke, as in a humanist letter.