What do we mean by 'selective breeding'?Explain?

Selective breeding is the process of choosing only some
animals to breed from a group. Imagine a farmer who has 25 cows. He wants to breed them
for the next generation. But he wants big, fat cows that give lots of milk and meat. So
he chooses the biggest, fattest bull and the milkiest cows and he selectively breeds
those. He does not breed his skinny
cows or aggressive bulls. So the next generation of his herd of cows is bigger and
fatter and milkier and more gentle.

Then, from that new
generation he selects the biggest, fattest bull and the milkiest cows and he selectively
breeds those....

Now repeat this many times. Generation
after genration of farmers select the cows and bulls which have the charecteristics that
they want until we have the modern cow, a very fat and milky peaceful animal which
produces the most meat and milk. 

(Selective breeding is
mankind's use of Natural Selection, a process of evolution.)