1. n. 
A group of salts formed by neutralization of phosphorous or phosphoric acid with a base, such as NaOH or KOH. Orthophosphates are phosphoric acid (H3PO4) salts, where 1, 2 or 3 of the hydrogen ions are neutralized. Neutralization with NaOH gives three sodium orthophosphates: (a) monosodium phosphate (MSP), (b) disodium phosphate (DSP) or (c) trisodium phosphate (TSP). Their solutions are buffers in the 4.6 to 12 pH range. TSP is an excellent degreaser. All will precipitate hardness ions such as calcium. Polyphosphates are polymers made from various orthophosphates by dehydration with heat. Sodium acid pyrophosphate (SAPP) is a clay deflocculant and treatment for cement contamination. For clay deflocculation, polyphosphates are limited by the temperature at which they hydrolyze back to orthophosphates, although several that performed up to 280°F [138°C] have been documented in the literature (see reference).
Sikorski CF and Weintritt DJ: "Polyphosphate Drilling-Mud Thinners Deserve Second Look," Oil & Gas Journal 81, no. 27 (July 4, 1983): 71-78.