any one of a series of oxyacids of phosphorus with the general formula Hn+2PnO3n+1. The first member is pyrophosphoric acid (n = 2) and the series includes the highly polymeric metaphosphoric acid. The higher acids exist in an equilibrium mixture
2.
a glassy or liquid mixture of orthophosphoric and polyphosphoric acids: used industrially as a dehydrating agent, catalyst, and oxidizing agent