heteronuclear multiple-bond correlation over two bonds 

Initialism: H2BC
https://doi.org/10.1351/goldbook.08353
Variant of the heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) experiment in nuclear magnetic resonance spectroscopy that almost exclusively correlates \(\ce{^{1}H}\) nuclei with heteronuclei separated by two covalent bonds.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 690 (https://doi.org/10.1515/pac-2019-0203)