Which type of signal is defined only at discrete moments and is commonly used in digital sampling?

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

Answer: (B)

Discretizing time is the essence here. In digital sampling, you take values of a signal only at specific time instants, typically t = nT, forming a sequence x[n]. That means the signal is defined only at those discrete moments, which is precisely what a discrete-time signal is. This time-domain discretization is what makes it practical for digital processing, storage, and transmission since a sequence of numbers represents the signal instead of a value for every moment in time.

Continuous-time signals, by contrast, exist for every moment in time. Analog signals are continuous in time (and often in amplitude). Digital signals usually refer to discrete amplitude levels, but the key distinction for this question is that the signal is defined at discrete time points, not every moment.