Cascade Transfer Function; Odd or Even Transfer Function
If the order $N$ of the system is even, you get $N/2$ second-order sections, where each second-order section combines either a pair of complex conjugate poles and zeros, or two real-valued poles and zeros. If $N$ is odd, you get $(N-1)/2$ second-order sections and one additional first-order section for the remaining real-valued pole and zero.