This type of circuit is called a bit slice. Many designers use clocks to provide synchronization of events. A clock is a circuit that emits a series of pulses with a determined width and interval. The clock cycle time is the time interval between two edges of a pulse. For purposes of precision, a crystal oscillator often controls clock frequency.
Many events can occur within one clock cycle.
For this reason, a single clock cycle must be broken down into subcycles. One way to do this is to tap the primary clock line and insert a circuit with a delay to create another signal that is simply a phase shifted replica of the first. Events can then tied to each edge of both pulses rise and fall. Sometimes one could be interested in an interval rather than an instant of the clock cycle. The combination of the primary clock and the delayed clock can once again come in handy by offering combinations of when the different clocks are rising and falling.