Angle
Geometric shape formed by two rays (initial and ending sides of the angle) that share a common endpoint called the vertex. You may name an angle using the vertex, or a point in each ray and the vertex label in the center.

Acute angle
An angle that is between 0 and 90 degrees.

Adjacent angles
If two angles have a common side, a common vertex and no common interior points then they are adjacent.

Collinear
In the same line.

Coplanar
Within the same plane.

Line
An infinite set of points that extends forever in two directions. 2 points on the line allows to uniquely define it.

Non-Collinear
Not in the same line.

Obtuse angle
An angle whose measure is greater than 90 but less than 180 degrees.

Plane
A two-dimensional group of points that goes on infinitely in all directions; made up of infinite lines

Point
Indicates a location in space and has no size. It is represented by a dot and usually labeled with uppercase letters. It is uniquely identified by a set of coordinates (x,y) in the plane, and (x,y,z) in the space.

Ray
The section of a line that has one endpoint in one side and it never ends at the other side. (flash light beam pointing to the space)

Segment
A section of a line, defined by two end points and all the points between them.