A line
The term you are describing is a line.
A straight line with no endpoints is a geometric concept that extends infinitely in both directions. It is often represented in mathematics by a line symbol, denoted by two points on the line or with a single letter. Unlike line segments, which have defined starting and ending points, a straight line has an infinite length and continues indefinitely without termination.
A line.
a line
line
The term you are describing is a line.
That's the definition of a "line".
line
A line.
A straight line without any defined end points
a line
line
In geometry, a line is a straight, one-dimensional figure that extends infinitely in both directions without any curvature. It has no endpoints and is defined by its length but not by its width or thickness. Lines can be described using equations in a coordinate system, and they are fundamental in defining shapes and angles in geometric constructions.
It would be a horizontal straight line, extending without end in both directions.
If you meant one direction, then it is a ray.
A straight line that touches a curve but continues without crossing it is called a "tangent." At the point of contact, the tangent line has the same slope as the curve, indicating that it just grazes the curve rather than intersecting it.
It is a tangent line