Definition
Horizontal
A level left-to-right direction in a chosen diagram or coordinate system.
What it means
On a normal page, horizontal runs across from left to right. It describes an orientation, not a kind of shape. On a coordinate grid, moving horizontally changes x while y stays the same.
Remember it
Across the page: x changes, y stays.
Example
The points (1, 4), (3, 4), and (7, 4) all have y-coordinate 4, so they lie on the horizontal line y = 4.
Watch for
A shape is not horizontal by itself. An edge, line, movement, or the shape’s orientation can be horizontal.
Common mix-up
Horizontal and vertical depend on the chosen diagram or axes; rotating a loose page can change what looks level.
Exact meaning
Horizontal describes a direction parallel to the chosen level left-to-right direction. On a standard coordinate plane, a horizontal line has a constant y-coordinate.