Signals defined at every instant in time are called what?

• A. Continuous-Time Signals
• B. Discrete-Time Signals
• C. Analog Signals
• D. Digital Signals

Answer: (A)

Signals that have a value for every real moment in time are continuous-time signals. Time is treated as a continuous axis, so you can describe or measure x(t) at any instant t, not just at a set of sampled moments. That’s what makes the signal continuous in time.

In contrast, discrete-time signals exist only at specific time instants, typically t = nT for integer n, which means values are defined only at those sample points and not for every moment in between. The terms analog and digital refer to the range of amplitude values, with analog being continuous-valued and digital being discrete-valued, but the defining distinction for this question is the continuity in time.