What is Pulses? Explain characteristics of pulse?

Here is the characteristics of a single pulse.

The voltage rises very rapidly from zero to its maximum value.
It stays steady at the maximum value for a time.
It then falls very rapidly back to zero.
The duration of a pulse can be anywhere from a very long time (days) to a very short time (picoseconds or less).
Pulses do not rise and fall instantaneously but take time (which may be very short).
They are called the RISE and FALL times.

If pulses occur one after another they are called a PULSE TRAIN.
The duration time of a pulse is called the MARK.
The time between pulses is called the SPACE.
The relative times are expressed as the MARK/SPACE RATIO.