A term which refers to the solid-state transformation of non-graphitic carbon into graphite by heat treatment under elevated pressure (e.g. 100 to 1000 MPa) so that a definitely higher degree of graphitization is achieved at lower temperature and/or for a shorter heat treatment time than in heat treatment of the same non-graphitic material at atmospheric pressure.
Source:
PAC, 1995, 67, 473. 'Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)' on page 495 (https://doi.org/10.1351/pac199567030473)