Lines in the diagram are represented by a line segment with arrows on both ends. We can identify two lines in the diagram: g and h.
However, only g is in the plane. We can also use any two points on a line to name it. Points X, Y, and Z are on the line, so we can also name it XZ. The order of X and Z does not matter and is, therefore, an arbitrary choice. By the same principle, another name for the line g is ZX.
