PPA stands for power, performance and area, and historically these have been the three variables used in deciding how to optimize semiconductor designs.
Until 65nm, cost, which is a function of area, and performance, were the most-cited criteria for a successful design. But as battery-driven mobile devices have replaced PCs as the volume platform for SoCs, power has moved up to the top of the list, followed by cost and performance. Performance is still critical in certain markets, such as servers, but even there more accountability for server power and cooling has made it imperative to reduce power.
With the Internet of Things market, companies are beginning to think of a fourth element to go with PPA, namely security.