When you get a voicemail and the person leaving the message sounds like a cross between Milton from Office Space and a constipated cat. For a more simple definition, when the person who leaves you a voicemail sounds like a retard.
Dude, what's up with your mom? I rammed my cock down her throat then after I left she sent me a voicefail. You should take her to the hospital and get her larynx checked out or something.