A discrete signal or discrete-time signal is a time series, perhaps a signal (information theory)|signal that has been sampling (information theory)|sampled from a continuous signal|continuous-time signal. Unlike a continuous-time signal, a discrete-time signal is not a function of a continuous-time argument, but is a sequence of quantities; that is, a function over a domain of discrete integers. Each value in the sequence is called a sample (signal)|sample.
When a discrete-time signal is a sequence corresponding to uniformly spaced times, it has an associated sampling rate; the sampling rate is not apparent in the data sequence, so may be associated as a separate data item.
A digital signal is a discrete-time signal that takes on only a discrete set of values. It typically derives from a discrete signal that has been quantization (signal processing) quantized.
Common practical digital signals are represented as 8-bit (256 levels), 16-bit (65,536 levels), 32-bit (4.3 billion levels), and so on, though any number of quantization levels is possible, not just power of two|powers of two.