heijastus

Heijastus is a Finnish noun meaning reflection, image, or echo, derived from the verb heijastaa (“to reflect”). The term is used both in everyday speech and in technical contexts.

In optics and acoustics, heijastus refers to the return of waves after striking a boundary—light or sound that bounces off surfaces—producing a reflected image or sound. In ordinary language, it also describes the image seen in a mirror or the reflection of a scene on calm water.

In mathematics and geometry, heijastus denotes a reflection transformation, an isometry that, with respect to a line (in two dimensions) or a plane (in three dimensions), preserves distances while reversing orientation. It is a basic symmetry operation alongside translations and rotations and is fundamental in the study of geometric figures and transformations.

In cultural and philosophical usage, heijastus is used metaphorically to describe how experiences, thoughts, or social conditions are reflected in literature, art, or discourse. The term thus spans both concrete physical phenomena and abstract conceptual reflections.

The word is common in Finnish technical and academic writing and is part of everyday vocabulary when discussing light, sound, or geometric symmetry. Its flexible meaning allows its use across science, art, and everyday language.