BIBO stability stands for which of the following?

• A. Bounded Input-Buffered Output
• B. Bound Input-Bounded Output
• C. Bounded Input-Bounded Output
• D. Boundless Input-Output

Answer: (C)

BIBO stability tests whether a system keeps its output finite when the input is finite in magnitude. The essential idea is: if every input that stays within some bound produces an output that also stays within some finite bound, the system is stable in the Bounded Input-Bounded Output sense.

The standard phrase is “Bounded Input-Bounded Output.” That’s why this is the best answer: it states clearly that a bounded input leads to a bounded output, with the bound on the output depending on the input bound but not on the particular signal.

To see why this concept matters, think of a stable system like a first-order low-pass filter: feed it a sine wave (which is bounded); the output remains a sine wave with finite amplitude. Contrast that with an integrator: even a bounded input can accumulate without bound over time, producing an unbounded output, which means it’s not BIBO stable.

So, the correct notion is that a system is BIBO stable if every bounded input yields a bounded output. The other phrasings don’t capture this standard idea.