The active ones means the active filters.An active filter is a type of analog electronic filter that uses active components such as an amplifier. Amplifiers included in a filter design can be used to improve the performance and predictability of a filter, while avoiding the need for inductors (which are typically expensive compared to other components).Active filters can implement the same transfer functions as passive filters,like high pass filter, low-pass filter,band -pass and notch filter.Of course the passive filters are those that uses only lumped components like coil, capacitors,resistors and transformers.