Successor
One more than a given whole number is called its successor.
Thus 1 is the successor of 0, 2 is the successor of 1 and so on.
0 is not the successor of any whole number.
Predecessor
One less than a given whole number(other than zero) is called its predecessor.
Thus 0 is the predecessor of 1, 1 is the predecessor of 2 and so on.
0 has no predecessor in the whole number system.