eclipsed (eclipsing)

https://doi.org/10.1351/goldbook.E01884
Two atoms or groups attached to adjacent atoms are said to be eclipsed if the @T06406@ between the three bonds is zero (or approximately so).
See:
bisecting conformation
,
eclipsing strain
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2206 [Terms] [Paper]