Orthogonal symmetric Lie algebra
In mathematics, an orthogonal symmetric Lie algebra is a pair ( g , s ) {\displaystyle ({\mathfrak {g}},s)} consisting of a real Lie algebra g {\displaystyle {\mathfrak {g}}} and an automorphism s {\displaystyle s} of g {\displaystyle {\mathfrak {g}}} of order 2 {\displaystyle 2} such that the eigenspace u {\displaystyle {\mathfrak {u}}} of s corresponding to 1 (i.e., the set u {\displaystyle {\mathfrak {u}}} of fixed points) is a compact subalgebra. If "compactness" is omitted, it is called a symmetric Lie algebra.
Source: Wikipedia — Orthogonal symmetric Lie algebra (CC BY-SA 4.0)