Signal edge

In electronics, a signal edge is a transition of a digital signal from low to high or from high to low:

• A rising edge (or positive edge) is the low-to-high transition.
• A falling edge (or negative edge) is the high-to-low transition.

In the case of a pulse, which consists of two edges:

• The leading edge (or front edge) is the first edge of the pulse.
• The trailing edge (or back edge) is the second edge of the pulse.