Filter is a frequency selection device, which can make the specific frequency components in the signal pass through, while greatly attenuating other frequency components.
The frequency selection effect of filter can be used to filter out the interference noise or carry on the spectrum analysis.
In other words, any device or system that can greatly attenuate or suppress a particular frequency component of a signal by passing through it is called a filter.
A filter is a device that filters waves.
"Wave" is a very broad physical concept. In the field of electronic technology, "wave" is narrowly limited to describe the process in which the values of various physical quantities fluctuate with time.
The process is converted into a time function of voltage or current through the action of various sensors, which is called the time waveform of various physical quantities, or the signal.
The independent variable time is continuously evaluated, so it is called continuous time Signal or Analog Signal habitually.
Filtering is an important concept in signal processing. In the DC stabilized voltage supply, the function of the filter circuit is to reduce the AC component in the pulsating DC voltage as much as possible and retain its DC component, so as to reduce the output voltage ripple coefficient and smooth the waveform.