I can't recall where I saw the 'BPA' first, but it stands for "Broadband Processor Architecture" apparentlly... it's an alias of the Cell architecture, which is distinguished from the Power architecture.
"Broadband Processor Architecture [BPA] is the formal name for the architecture of the Cell family of processors," said Brandow. "BPA extends the Power architecture with coherent off-load accelerators and real-time management functions."