A polyatomic (non-linear) molecule (like NH3) can rotate about any of three co-ordinate dimension. As it has 6 degrees of freedom, 3 rotational and 3 translational. At normal temperature a polyatomic gas molecule has vibration energy greater than that of a perfect gas. The atoms within the particle may also vibrate with respect to every other at high temperature. In that case, the particle will have an additional degree of freedom, with reference to vibration motion.
Degree of freedom, f = 6 (3 translational +3 rotational) at room temperature
f = 8 (3 translational+3 rotational+2 vibration) at high temperature