Lie superalgebra
In physics the letter "P" is used for a basis of the even bosonic part of the Lie superalgebra, and the letter "Q" is often used for a basis of the complexification of the odd fermionic part, so in particular the structure constants of the Lie superalgebra may be complex rather than real. Often the basis elements "Q" come in complex conjugate pairs, so the real subspace can be recovered as the fixed points of complex conjugation.