This graph shows a downward-opening parabola, indicating that it represents a quadratic function with a maximum value at its vertex. Observing the graph, we see that the vertex occurs at the point $(0, 5)$.

Thus, the maximum value of this function is: $\text{Maximum value} = 5$

Would you like more details or have any other questions?

Here are some related questions to expand your understanding:

1. What is the general form of a quadratic function, and how can you determine if it opens up or down?
2. How do you calculate the vertex of a quadratic function given in standard form?
3. Why is the vertex the maximum point for a downward-opening parabola?
4. Can there be other points on the graph that have the same $y$-value as the maximum value?
5. How would the maximum value change if we translated the graph up or down?

Tip: For a parabola of the form $y = ax^2 + bx + c$, if $a < 0$, it opens downward and has a maximum value at its vertex.