solid-state nuclear magnetic resonance spectroscopy 

Initialism: SSNMR
https://doi.org/10.1351/goldbook.08415
Application of nuclear magnetic resonance spectroscopy to solids.
Note:
SSNMR is characterized by the presence of anisotropic (directionally dependent) interactions. Chemical shift anisotropy (CSA) and internuclear dipolar coupling result in severe line-broadening of the corresponding NMR signals and specific hardware and methods are required to perform SSNMR to mitigate some of these issues including magic angle spinning (MAS).
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 704 (https://doi.org/10.1515/pac-2019-0203)