Vocabulary

Acute Angle - an angle that measures less than 90 degrees.

Acute Triangle - a triangle where all angles measure less than 90 degrees.

Adjacent Angles - adjacent means 'next to'. So adjacent angles are 2 angles 'next to' each other. (They must share a side and vertex, but canít occupy the same space)

Angle - the intersection of two rays that have a common endpoint.

Angle Bisector - a ray or segment that divides an angle into 2 congruent or equal angles.

Bisect - dividing something into two equal parts.

Collinear - when points lie on the same line.

Complementary Angles - two angles that add up to 90 degrees.

Congruency/Congruent - when two objects have the same shape and size. (I tend to just think that congruent objects are the same or equal).

Coplanar - when points lie on the same plane.

Distance - is the numerical description of how far apart objects are.

Equiangular Triangle - a triangle where all angles are equal. Since all triangle equal 180 degrees and all triangles have 3 angles. If you divide the total measure of 180 degrees by 3 angles, you get 60 degrees for each angle. All equiangular triangles have interior angles always equaling 60 degrees. 'Equi' means equal and 'angular' means angles. Equiangular triangles are also equilateral triangles. Since all interior angles are equal, all sides opposite each angle is also equal.

Equilateral Triangle - this is a triangle where all sides are equal to each other. 'Equi' means equal and 'lateral' means side so 'equilateral' means equal sides. Equilateral triangles are also equiangular triangles. Since all sides are equal, all angles opposite each side has to be equal to each other as well.

Isosceles Triangle - this is a triangle where at least two sides are equal.

Line - a collection of straight points with no thickness or width that has infinite length. In a figure, a line is shown with arrows on both ends.
line

Line Segment - is part of a line. You can measure the length of a line segment. In a figure, it is a line with two endpoints or dots, one at each end.
line segment

Linear Pairs - two adjacent angles that create line.

Midpoint - is the middle point of a line segment.

Obtuse Angle - an angle that measures more than 90 degrees.

Obtuse Triangle - a triangle where one angle measures more than 90 degrees.

Plane - a two-dimensional surface with no thickness that has infinite length and width. (It would be like a piece of paper that has infinite length and width and has no thinkness.)
plane

Point - a location in space with no thickness. It has no measure, weight, color, etc. It just indicates a location. In a figure, it is marked as a dot.
point

Ray - or half-line, is part of a line that is finite in one direction but infinite in the other. In a figure, one end has an endpoint and the other end of the figure has a line with an arrow on it indicating that portion of the line goes on forever. (I always imagine a sun ray where the sun is the endpoint and the sun ray travels on forever in the other direction. The same idea follows for if you were holding a flashlight.)
ray

Right Angle - an angle that measures exactly 90 degrees.

Right Triangle - a triangle that has one angle that measures exactly 90 degrees.

Scalene Triangle - this is a triangle where no sides are equal.

Skew - lines on a different plane that don't intersect and are not parallel. (Think of it as two different powerlines at different heights going in different directions.)

Supplementary Angles - two angles that add up to 180 degrees.

Transversal - a line that intersect two or more lines. Often times the lines transversals cross are parallel lines.

Vertex - the common endpoint on an angle.

Vertical Angles - two nonadjacent angles formed by two intersecting lines. Vertical angles are opposite of each other when 2 lines cross and are always congruent.