The first part of your question is easy to answer: a biquad[ratic] filter is simply a filter that has two poles and two zeroes. Essentially, the discrete time transfer function has a quadratic numerator and a quadratic denominator.
I'm afraid I have not implemented one in real-time so can't comment on the second part of your question relating to pipelining retiming!
Perhaps you might gain insight from Miloš Drutarovský's paper "An Implementation of High Performance IIR Filtration on 2-MAC Blackfin DSP Architecture"
Article An Implementation of High Performance IIR Filtration on 2-MA...