What does 'yan tan tether' mean?

‘yan tan tether’ is an old English way of counting sheep ’1,2,3′:

 

“Yan, tan, tether, mether, pimp
Sether, hether, hother dother, dick
Yan dick, tan dick, mether dick, bumfit
Yan bumfit, tan bumfit, tether bumfit, mether bumfit, gigot”.
 

yan = 1
tan = 2
tether = 3
mether = 4
pimp = 5
Sether = 6
hether = 7
hother = 8
dother = 9
dick = 10
Yan dick = 11
tan dick = 12
tether dick = 13
mether dick = 14
bumfit = 15
Yan bumfit = 16
tan bumfit = 17
tether bumfit = 18
mether bumfit = 19
gigot = 20
 

 
It’s a great poem for kids. If yours start reciting it, do let us know as we’d love to hear it in action!