Option A asymptote.
Asymptotes are lines to which the graph approaches very it can come very close to it but will never touch it. Asymptote are the limits of a graph.
IN the given graph of Hyperbola the two blue lines representing the Hyperbola are coming too close to the red lines but not touching it .
The two red lines are called the Asymptotoes of the Hyprbola.It is the limit of the Hyperbola.