réflexion

Réflexion is a French noun that covers multiple related ideas. It can refer to cognitive activity—the act of thinking carefully, examining a matter, or engaging in introspection. It can also describe the return or bouncing back of waves, such as light, sound, or heat, when they meet and rebound from a surface.

Etymology and usage: The term comes from the Latin reflectere, meaning to bend back or turn back. In contemporary French, réflexion is used for both mental processes and physical phenomena involving returning waves. In English, the corresponding term is reflection; reflexion is an archaic or less common form.

Philosophical and educational contexts: In philosophy, reflection denotes deliberate contemplation about ideas, values, or experiences. In psychology and education, reflective practice refers to the systematic consideration of one's own experiences to improve decision making, understanding, and professional performance.

Optics and geometry: In optics, reflection is the change in direction of a wave at a boundary, following the law of reflection: the angle of incidence equals the angle of reflection with respect to the surface normal. Surfaces can produce specular (mirror-like) or diffuse reflection. In geometry, a reflection is a symmetry that maps figures to their mirror images across a line (in two dimensions) or a plane (in three dimensions), and a point reflection is a central symmetry about a point.

Other usages: The term also appears in literary and ethical discussions as a metaphor for careful consideration of one’s actions or beliefs. In English, the standard spelling is reflection; réflexions are the French form of the same concept.