What is a bass ukulele called?

A bass ukulele is called simply that - a bass ukulele.  The first commercial bass ukes were from Kala, who still call them U-bass or Ubass.  For some folks the name has stuck - a little like 'Hoover' meaning vacuum cleaner. At Buzzards Field we call them short scale bass ukuleles as the kits we supply create instruments a little larger than Ubass, but much smaller than traditional bass guitars - despite producing authentic bass frequencies (unlike some metal stringed bass ukes).
Buzzards Field sell a kit which allows a small classical guitar to become a short scale bass ukulele and accept bass ukulele strings.