To determine if a relation defines $y$ as a function of $x$, we can apply the Vertical Line Test. This test states that a relation is a function if, and only if, no vertical line intersects the graph at more than one point.

From the graph you provided:

• The curve oscillates in a wave-like pattern, crossing the $x$-axis multiple times.
• At no point does a vertical line intersect the curve at more than one point.

Since any vertical line drawn on this graph will only touch the curve at one point, this relation does define $y$ as a function of $x$.

Would you like a more detailed explanation on the Vertical Line Test or how functions work? Here are some related questions you might want to explore:

1. How does the Vertical Line Test work for different types of graphs?
2. What is the difference between a function and a relation?
3. How can we determine if a relation is one-to-one (injective)?
4. What happens if a vertical line touches a graph at multiple points?
5. How does the concept of a function apply to real-world situations?

Tip: Always remember, for a graph to represent a function, each input (value of $x$) must correspond to exactly one output (value of $y$).