Under Â§ 1505, however, a defendant can be convicted of obstruction of justice by obstructing a pending proceeding before Congress or a federal agency. A pending proceeding could include an informal investigation by an executive agency.
Piecewise is actually a way of expressing the function, rather than a characteristic of the function itself, but with additional qualification, it can describe the nature of the function.
1 Piecewise functions are defined using the common functional notation, where the body of the function is an array of functions and associated subdomains.  The absolute value, $\left | x \right |$ is a very common piecewise function. For a real number, its value is $-x$ when $x<0$ and its value is $x$ when $x\geq0$.