three-dimensional nuclear magnetic resonance spectroscopy 

Synonym: 3-D NMR
https://doi.org/10.1351/goldbook.08432
Measurement method of nuclear magnetic resonance spectroscopy in which data are collected in three time domains.
Note:
A 3-D NMR experiment may be constructed from a 2-D NMR experiment by inserting an additional indirect evolution time and a second mixing period between the first mixing period and the direct data acquisition.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 708 [Terms] [Paper]