Sequential Logic

A sequential logic circuit implements a function using the notion of circuit state along with the usual logic components such as OR gates, NOT gates, etc. This circuit state is a function of past inputs and is implemented by some form of memory. So we can say that in a sequential logic circuit, outputs are a function of current inputs and past inputs. This is in contrast with combinational logic where the circuit has no notion of past inputs — its outputs are a function solely of current inputs.

The SR flip-flop is an example of a sequential logic circuit.

References

Kleitz, W. Digital Microprocessor Fundamentals. 3rd Edition. Prentice Hall, 2000.
Mano, M. Morris, and Kime, Charles R. Logic and Computer Design Fundamentals. 2nd Edition. Prentice Hall, 2000.