Salts or esters of cyclic polyphosphoric acids are often called "metaphosphates". What are commonly called trimetaphosphates actually have a mixture of ring sizes. A general formula for such cyclic compounds is  where x = number of phosphoric units in the molecule.
When metaphosphoric acids lose their hydrogens as , cyclic anions called metaphosphates are formed.  An example of a compound with such an anion is sodium hexametaphosphate (), used as a sequestrant and a food additive.