In Digital circuit theory, sequential logic is a type of logic circuit whose output depends not only on the present input bit also on the history of the input. This is in contract to combinational logic, whose output is a function of, and of, the present input.
In other words , sequential logic circuit, has storage (memory) while combinational logic does not. Sequential logic circuit can be classified into two broad categories.
1. Asynchronous (or without clock) Sequential circuit
2. Synchronous (or clocked) sequential circuit.
Here Filp-Flop, Timer, Register and counter are most common example of there sequential circuit,