geo vocab

Basic Terms

• Point – A location with no size or dimension.

• Line – A straight path that extends infinitely in both directions.

• Line Segment – A part of a line with two endpoints.

• Ray – A part of a line that starts at one point and extends forever in one direction.

• Plane – A flat surface that extends infinitely in all directions.

Angles

• Angle – Formed by two rays with a common endpoint (vertex).

• Acute Angle – Less than 90°.

• Right Angle – Exactly 90°.

• Obtuse Angle – Greater than 90° but less than 180°.

• Straight Angle – Exactly 180°.

• Complementary Angles – Two angles that add up to 90°.

• Supplementary Angles – Two angles that add up to 180°.

• Vertical Angles – Angles opposite each other when two lines cross (always equal).

• Adjacent Angles – Angles that share a side and a vertex.

Lines & Relationships

• Parallel Lines – Lines that never intersect and are always the same distance apart.

• Perpendicular Lines – Lines that intersect at a 90° angle.

• Transversal – A line that intersects two or more lines.

Shapes & Polygons

• Polygon – A closed figure made of straight lines.

• Triangle – A polygon with 3 sides.
  

  • Equilateral Triangle – All sides and angles are equal.

  • Isosceles Triangle – Two sides and two angles are equal.

  • Scalene Triangle – No sides or angles are equal.

  • Right Triangle – Has one 90° angle.

• Quadrilateral – A polygon with 4 sides.
  

  • Parallelogram – Opposite sides are parallel and equal.

  • Rectangle – All angles are 90°, opposite sides are equal.

  • Square – All sides and angles are equal (90°).

  • Rhombus – All sides are equal, opposite angles are equal.

  • Trapezoid – One pair of parallel sides.

Measurements

• Perimeter – The distance around a shape.

• Area – The space inside a shape.

• Volume – The amount of space inside a 3D object.

• Circumference – The distance around a circle.

• Radius – Distance from the center of a circle to the edge.

• Diameter – Distance across a circle through the center.

• Pi (π) – A constant ~3.14 used in circle calculations.

Transformations

• Translation – Sliding a shape without rotating or flipping it.

• Rotation – Turning a shape around a point.

• Reflection – Flipping a shape over a line (mirror image).

• Dilation – Making a shape larger or smaller while keeping its shape.

Other Important Terms

• Congruent – Exactly the same shape and size.

• Similar – Same shape but different sizes (angles stay the same).

• Hypotenuse – The longest side of a right triangle (opposite the right angle).

• Pythagorean Theorem – In a right triangle:
  a^2 + b^2 = c^2

• Tessellation – A pattern of shapes that fit perfectly together without gaps.