for the first time in many years we are without a pembroke corgi,having lost our wee man on June 16th, we had no option he was such a brave boy it would not have been fair to him, so!!!!.
my question is can anyone explain what is natural bob tail?

A natural bobtail is one that is born naturally with a short tail :d  Hoipe this helps.  There are a number of breeds that can be born naturally with short tails, mine included.

and the pembroke corgi's bobtail is the one that they used to create the
Boxer bobtail :)