Basic geometry: language and labels
Notes from Khan Academy video Basic geometry: language and labels  Introduction to Euclidean geometry  Geometry  Khan Academy
 Word geometry is made up of 2 components: "geo" and "metry":
 "Geo"  earth
 "metry"  measurement
 Therefore, geometery is about how shapes and space (things we see) related to each other.
Plane
 A Plane is a flat surface that has 2 dimensions: width and height and goes on infinity in either direction.
Point

A Point refers to a dot on that plane and is the most basic geometric idea.
 Points are commonly labelled using upper case letters: A, B, C, D etc
 Point is said to be 0dimension: it doesn't provide any direction information.
Line Segment

A line that connects 2 points, is referred to as a Line Segment
 A line segment is described using its endpoints: the points that it is connected by.

In math notation, a line is drawn over the endpoints to denote that it's a line segment.
$\overline{AB}$

The endpoints of a line segment can be inversed:
$\overline{AB} = \overline{BA}$

Is onedimension  you can move back and forth along it.
Ray

A line that starts from one point that continues on infinitely in one direction is called a Ray

The order of a ray is meaninful, unlike a line segment, as it describes the direction of the ray:
$\overrightarrow{AB} \neq \overrightarrow{BA}$

The starting point is referred to the endpoint.

Line

A line that continues infinitely in either direction is formally called a Line.

A line is described by the endpoints it intersects, typically in alphabetical order though the order does not matter.
$\overleftrightarrow{AB} = \overleftrightarrow{BA}$

Collinear points

If you have a line segment and introduce a point in the middle, you could describe all 3 points as "Colinear"  they sit on the same line.

In the above picture, if the distance between $XZ$ was the same as the distance between $ZX$, then you would refer to Z as the midpoint of the line segment $XY$.