A Mini Windjammer is simple lined fur cover to fit over the microphone directly or its foam gag. They are used on and off of camcorders to provide a cheap and effective protection against wind noise.
Wind-noise is an inherent problem with all microphones. You can hear it as a low rumble, a loud fluttering or, if the noise overloads any part of the sound chain, serious distortion. Some microphone designs are more susceptible than others but it is always essential touse a wind-noise reduction system - a wind-gag - whenever there is any amount of wind or air movement.