Line

In geometry a line:

is straight (no curves),
has no thickness, and
extends in both directions without end (infinitely).

A line has no ends!

Play With It

Change the position of points A and B. Note that line AB extends forever in both directions:

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Line Segment

If it does have ends it is called a "Line Segment".

Ray

ray
If it has just one end it is called a "Ray"

This is Cool

Now play with this one ... point "B" is made to always be an equal distance from point "A" and "C". The result is a line (all the possible position of point "B" make a line):

Point, Line, Plane and Solid

A point has no dimensions, only location
A line is one-dimensional
A plane is two dimensional
A solid is three-dimensional