1. Any phosphate of calcium. 2. Any of the following three calcium orthophosphates, all of which are white or colorless in pure form: Ca(H₂PO₄)₂ is used as a fertilizer, as a plastics stabilizer, and in baking powder, and is also known as acid calcium phosphate, calcium dihydrogen phosphate, monobasic calcium phosphate, monocalcium phosphate; CaHPO₄ is used in pharmaceuticals, animal feeds, and toothpastes, and is also known as calcium hydrogen phosphate, dibasic calcium phosphate, dicalcium orthophosphate, dicalcium phosphate; Ca₃(PO₄)₂ is used as a fertilizer, and is also known as tribasic calcium phosphate, tricalcium phosphate.