13:10 Karsus Ren 226 1 5 83% accept rate feedback 1 Answer active oldest votes up vote 5 down vote accepted The "s" stands for special . Lie algebras are usually named after Lie groups. $\text{U}(2)$ and $\text{SU}(2)$ have different Lie algebras so they're named $\mathfrak{u}(2)$ and $\mathfrak{su}(2)$, but as it