I looked around a bit and found some information.
My understanding is that it is a tax on residents of Kenya who operate small to medium size businesses.
You can go to the Kenya Revenue site
http://www.kra.go.ke/
In the right hand column under "domestic taxes"
there is a link to "Turn Over Tax"
When you click on the link it will give you a pdf
leaflet/brochure that gives more details.
