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Geometry Definitions

The table below covers most of the words and terminology that you'll be using for your various Geometry topics.

Word or Phrase Definition
Angle When 2 rays have a single endpoint, they form what looks like a corner of sorts. The inside of this corner is called its angle.
Point A point is a place for one single position and contains no length (as a line would. For 2D shapes (squares, triangles, etc), a point consists of an X and a Y. For 3D shapes (cubes, spheres, etc), a point will have X, Y, and a Z value.
Area The area is the amount of space inside of the shape. For example, the area of a square is all the space that is inside of the square. This is used for 2D shapes. For 3D shapes see Surface Area and Volume.
Surface Area Surface Area is used for 3D shapes to describe how much "outter surface" the shape has. For example, imagine you are holding a baseball. The surface area is all the area you can touch.
Volume Roughly the opposite of Surface Area, the volume of a 3D shape is the space inside of a shape that you cannot touch. If you have a can of soda, the amount of liquid inside of the can is the volume; the parts of the can you can touch is the surface area.
Parallel Lines Two different lines with the same slope. Since the lines have the same slope (and are not equal), they will never touch (intersect) each other, and are therefore parallel.
Congruent A fancy word for "equals." Two polygons are congruent if they are the same size and shape. They may be rotated differently, but they if their sizes and shape are equal, they are congruent.
Line A line is continuous path that continues forever (to infinity) in each direction it is pointing.
Line Segment A line segment is a piece of a line or ray, containing two distinct endpoints.
Ray A ray is a line that only continues to infinity in one and only one direction. The other end of the ray is an endpoint.
Intersecting Lines Two lines that are not parallel. That is, two lines who have their paths cross and have a common point, called their "intersection."
Transveral Line A line that intersects two other lines.
Vertex The point (angle) where two lines (rays, or line segments) intersect.
Supplementary Angles Two angles whose sum add up to 180 degrees

Now that we're doing learning our new lingo, let's get started on the basics, Using and Classifying Lines. Have another topic in mind? Find it in our Math Lessons or go back to the Lesson and Tutorial Center!


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