l, u

https://doi.org/10.1351/goldbook.L03423
Stereodescriptors of @D01679@ with two @C01061@. When the two @C01058@ elements are both R or both S the @M03986@ is described as having an l relationship (l = like), when one @C01061@ is R and the other S the molecular entity is described as having a u relationship (u = unlike). The notation can be extended to molecules with more than two @C01058@ elements whereby the l, u relationships of the @C01057@ elements are considered in pairs.
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2211 [Terms] [Paper]