Notes

A point in geometry is a location. It has no size i.e. no width, no length and no depth. A point is shown by a dot. Aline is defined as a line of points that extends infinitely in two directions point is a primitive notion upon which the geometry is built.
A long thin mark made by a pen, pencil, etc. In geometry a line is straight (no curves), has no thickness, and extends in both directions without end (infinitely)
A part of a figure cut off by a line or plane intersecting it, in particular.
A portion of a line which starts at a point and goes off in a particular direction to infinity.
A flat surface that is infinitely large and with zero thickness.
Three of more points , , , ..., are said to be collinear if they lie on a single straight line. A line on which points lie, especially if it is related to a geometric figure such as a triangle, is sometimes called an axis.
In the same plane.
In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.
Parallel lines are two lines that are always the same distance apart and never touch. In order for two lines to be parallel, they must be drawn in the same plane, a perfectly flat surface like a a wall or sheet of paper.
Perpendicular means "at the right angles". A line meeting another at the right angle, or 90* is said to be perpendicular to it.
In three-dimensional geometry, skew lines are two lines that do not intersect and are not parallel. A simple example of a pair of skew lines is the pair of lines through the opposite edges of a regular tetrahedron.
A circle is a shape with all points the same distance from its center. A circle is named by its center.