1. The problem asks for the domain of the function $y = \cos(x)$.\n\n2. The domain of a function is the set of all possible input values ($x$) for which the function is defined.\n\n3. The cosine function $\cos(x)$ is defined for all real numbers $x$. This means you can input any real number into $\cos(x)$ and get a valid output.\n\n4. Therefore, the domain of $y = \cos(x)$ is $(-\infty, \infty)$.\n\n5. Among the given options, option B corresponds to $(-\infty, \infty)$, which is the correct domain of the cosine function.