Extraction in which both phases are continuously added (or changed) and flow (or move) in opposite directions as the extraction progresses.
Note: The phases are either immiscible or separated by a membrane.
Source:
PAC, 2016, 88, 517. 'Glossary of terms used in extraction (IUPAC Recommendations 2016)' on page 522 (https://doi.org/10.1515/pac-2015-0903)