A notch filter is a filter that filters out a particular frequency from a signal. So say i have a a bunch of signals with many frequencies from 1-100hz and send it through a notch-filter designed to filter 50hz i would notice that the signals around the 50hz get a lot weaker. So in the Frequency spectrum a "Notch" appears in the middle! Hence Notch-filters!
You may think "what is the use of that?" so here is a Application example:
Say you have a audio-amplifier with a simple power-supply connected to your main. Because the main tends to alternate at 50-60hz it is possible that tiny distortion from your supply gets in your audio amplifier (causing sound to Hum). By using a Notch filter designed to filter out 60hz you can remove the unwanted Hum!
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If you Google Band Pass Filter you will get all the information you want.
They take out the signal above and below the frequency you want.
I think the term Notch Filter (Band Pass Filter) and H bridge Circuit (Full Bridge Circuit) come from the same source. The Net and the use of trade terms, added to that, terms from one part of the world being used in other parts of the world.
Remember this is the WWW, if you look at schematics on the net and circuit simulator programs you will find hundreds of symbols just for one component, so it is no surprise there is more than one term for a circuit or more than one symbol for a component.
Any way they have a number of uses from tuners in radios to equalizers and stereo systems.
I hope this helps you Joe
Another easy to find answer on wikipedia for you: http://en.wikipedia.org/wiki/Band-stop_filter
Is your internet search engine of choice broken?