An even function is defined by the property that f(-x) = f(x) for all x in the domain of f. This means that the function has the same output for both positive and negative inputs of the same magnitude.
The graph of an even function exhibits symmetry about the y-axis. This means that if you were to fold the graph along the y-axis, both halves would match perfectly. A common example of an even function is f(x) = x². If you plot this function, you will observe that both sides of the graph are mirror images of each other with respect to the y-axis.
Thus, the type of symmetry that the graph of an even function has is y-axis symmetry.