Define the Signals in Time Domain?

The time domain is the type of visualization that most people are familiar with. This method shows variations of a signal with time. The most common time domain instrument is the oscilloscope, which has graduations of volts on the Y-axis and graduations of time on the X-axis. A pure sine wave is shown on the left side of the above diagram. The signal has a frequency (the number of times that the signal repeats itself in a second) and a period (the time duration of one complete signal cycle).

Frequency and period are not diverse quantities, but diverse methods of describing the time measurement of the same signal. The figure shows two waveforms. The lower one has a higher frequency (more cycles per second) and a shorter period (less time to complete one cycle). Both of the signals have similar amplitude.