Meta-, Ortho-, Para-

(abbreviated m-, o-, p-), prefixes used in organic chemistry to designate the position of two identical or different substituents relative to each other in a benzene ring. For example, substituents in meta- compounds are located in the 1,3 positions, those in ortho- compounds occupy the 1,2 positions, and those in para- compounds are in the 1,4 positions:

In inorganic chemistry, the prefixes meta- and ortho- are used to designate types of acids that differ in the number of hydroxyl groups (ortho- means the greatest number, and meta-, the smallest)—for example, orthophosphoric acid, H₃PO₄ and meta-phosphoric acid, HPO₃.