90 degrees. :

Perpendicular Line: at right angle(s) with another surface

Paralell Line. Lines running a constant distance from one another, never intersecting in the same direction. but running in the same direction.

Line segment: A segment of line.

Reflex Angle: an angle between 180 and 360 degrees.

Convex Polygon. A polygon where every diagonal lies inside this figure.

e.g: rhombus, regular polygons, triangles.

Concave Polygona polygon where at least one diagonal lies outside the figure (also called a non-convex polygon)

a quadrilateral with both pairs of opposite sides parallel and all sides equal; a parallelogram with two adjacent sides equal in length

a five-sided polygon

A regular pentagon has all its sides and angles equal. Angles ad up to 540 degrees

Diameter:a line interval passing through a circle’s centre with its end points on the circumference

The diameter is twice as long as the circle’s radius.

Tetrahedra: a solid comprised of four triangular faces; a triangular pyramid

A regular tetrahedron (one of the five Platonic solids) has four congruent equilateral triangles as faces.

Regular polyhedra: A regular polyhedron is a polyhedron whose symmetry group acts transitively on its flags. A regular polyhedron is highly symmetrical, being all of edge-transitive, vertex-transitive and face-transitive.

Pentahedra: In geometry, a pentahedron (plural: pentahedra) is a polyhedron with five faces or sides. There are no face-transitive polyhedra with five sides and there are two distinct topological types.

Cubes; a symmetrical three-dimensional shape, either solid or hollow, contained by six equal squares.

Prisms: a solid geometric figure whose two ends are similar, equal, and parallel rectilinear figures, and whose sides are parallelograms.

dodecahedron: a three-dimensional shape having twelve plane faces, in particular a regular solid figure with twelve equal pentagonal faces.

icosahedron: a three-dimensional shape having twelve plane faces, in particular a regular solid figure with twelve equal pentagonal faces.

cylinders: a solid geometrical figure with straight parallel sides and a circular or oval cross section.
a solid or hollow body, object, or part having the shape of a cylinder.

pyramid: a solid geometrical figure with straight parallel sides and a circular or oval cross section.
a solid or hollow body, object, or part having the shape of a cylinder.

Vertex: in 2D shapes, a point where two straight lines meet to make an angle;
in 3D objects, a point where three or more straight edges meet to make a corner