Altitude

Altitude [al-ti-tyood]
Noun
The altitude (also known as the height) is line at right angle to a side that goes through the oposite vertex.

* Blue line is the altitude while the red lines are the triangle's edges. 

Vanishing Point

Vanishing Point [van-ish-ing point]
Noun
A vanishing point is a a certain location in a perspective drawing which receding parallel line, depending on how viewed, can alternate perspective. Allows a shape or figure to appear faintly closer or further (smaller/bigger) depending on how close and how it is placed in coloration with the vanishing point.      

Perspective Drawing

Perspective Drawing [per-spek-tiv draw-ing]
Noun
Perspective drawing is an accurate portrayal on a flat surface (usually facilitated by an isometric dot paper) of an image seen by the eyes. This type of drawing primarily focuses on perspective points and vanishing points on the paper,  allowing images to appear closer or further based on the designated drawing.

This is extremely important in geometry, for it allows one to create a clear representations of a 3D solid figure (usually very hard achieve).     

Isometric Dot Paper

Isometric Dot Paper [ahy-suh-me-trik dot pey-per]
Noun
An isometric dot paper (also known as 3D paper) is a type of graph paper which allows for more accurate drawing of solid figures. By having small dots all over the paper, it allows for the user to connect the dots, crating both edges and vertices with more facility.  

Diagonal

Diagonal [dahy-ag-uh-nl]
Noun
A diagonal is a straight line inside a shape that goes from one vertex to another (cannot intersect an edge). When we join two vertices of a polygon which isn't already joined by an edge, we get a diagonal.

*Both dotted lines are indeed diagonals 

Parallel Planes

Parallel Planes [par-uh-lel pleyn]
Noun
Parallel planes are planes that do not intersect and are indeed parallel. Two planes that aren't parallel (intersecting planes) intersect at a line.

An example of parallel planes are the walls and floor of a room; never intersecting.  

Platonic Solid

Platonic Solid [pluh-ton-ik sol-id]
Noun
A platonic solid is a 3D shape which has the following characteristics:

• each face is the same exact polygon 
• the same number of polygon meet at each vertex/corner   

Tetrahedron 3 triangles meet at each vertex 4 Faces 4 Vertices 6 Edges

Cube 3 squares meet at each vertex 6 Faces 8 Vertices 12 Edges