vertical line (undefined slope)
recta vertical (pendiente indefinida)
a line that goes straight up and down; its slope is undefined and its equation is x = c.
Example
The line through (3, 1) and (3, 9) is x = 3; its run is 0, and you can't divide by 0.
In Spanish
recta vertical (pendiente indefinida) — una recta que va derecho hacia arriba y hacia abajo; su pendiente es indefinida y su ecuación es x = c.
La recta que pasa por (3, 1) y (3, 9) es x = 3; su avance es 0 y no se puede dividir entre 0.