Even Function: $f(x)$ is even if $f(-x) = f(x)$ for all $x$ in its domain, and its graph is symmetric about the y-axis.
Symmetry:A property where one part of a figure or graph can be transformed into another part by some operation such as reflection or rotation.
$\int_{-a}^{a} f(x) \, dx$: This represents the definite integral of a function from $-a$ to $a$. For an odd function, this value equals zero.