# Euclidean geometry

From Citizendium, the Citizens' Compendium

**Euclidean geometry** is a form of geometry first codified by Euclid in his series of thirteen books, The Elements.

## Concepts

Some of the concepts used and described in Euclidean geometry are:

- A
**point**is a mathematical object which has a position but neither length nor breadth nor depth. - line or
**straight line** - surface
- plane
- plane angle
- rectilinear angle or
**angle**including - parallel
- perpendicular
- boundary
- figure
- plane figure
- circle
- center
- diameter
- semicircle
- trilateral
- quadrilateral
- multilateral
- equilateral
- congruence
- similarity
- rigid motion
- dilation