Theory:

Line parallel to the \(x\) - axis:
 
Consider drawing a line parallel to the \(x\) - axis. If the distance from the \(x\) - axis and the line is the same, then the line can be represented as \(y = c\) (where \(c\) is a constant).
 
Line parallel to the \(y\) - axis:
 
Consider drawing a line parallel to the \(y\) - axis and the distance between the \(y\) - axis and the line is the same, then the line can be represented as \(x = c\) (where \(c\) is a constant).
Example:
Consider plotting the points \((-1,2)\), \((0,2)\), \((1,2)\), \((2,2)\), and \((3,2)\) and joining them. We get a straight line.
 
1259_12.png
 
Since the points are at the same distance (\(2 \ cm\)) from \(x\) - axis. Then, the line is parallel to the \(x\) - axis.