A parallelogram is a quadrilateral with two pairs of parallel sides. The opposite sides of a parallelogram are of equal length and the opposite angles are of equal measure.
Any three points, when non-collinear, determine a unique triangle and a unique plane. A triangle has three sides and three angles. The three angles always add to 180°.
A circle is the set of all points in a plane that are at a given distance from a given point. It is the curve traced out by a point that moves so that its distance from a given point is constant.
A polygon is a plane 2D shape that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain. These segments are called its sides.
A convex quadrilateral with at least one pair of parallel sides is referred to as a trapezoid in American and Canadian English but as a trapezium in English outside North America.
A rhombus is a simple quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length.
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cylinder is one of the most basic curvilinear geometric shapes whose surface is formed by the points at a fixed distance from a given straight line, the axis of the cylinder.
An ellipse is a curve on a plane that surrounds two focal points such that the sum of the distances to the two focal points is constant for every point on the curve.
Analytic geometry is the study of geometry using a coordinate system. It is frequently used in physics and engineering, and is the foundation of most modern fields of geometry.