A polynomial is an algebric expression, eg: x²+1. Only non negative integers i.e positive integers are only the exponent of the variable. The exponent of variables are always positive. Power can negative, the value of a negative exponent for variable is not defined. 
Polynomial define as it is a algebraic expression where the exponents are non negative integrs and the exponents are not in the form of fraction

Non negative integers means the bases should have exponents with positive numbers
1 1 1