The Butterworth filter is a type of signal processing filter designed to have as flat a frequency response as possible in the passband. It is also referred to as a maximally flat magnitude filter. It was first described in 1930 by the British engineer Stephen Butterworth in his paper entitled "On the Theory of Filter Amplifiers".
Read more about Butterworth Filter: Original Paper, Overview, Example, Transfer Function, Filter Design, Comparison With Other Linear Filters