Complex sentence: In characteristic other than 2, these are equivalent (in the presence of bilinearity), so this distinction doesn't arise when considering real or complex Lie algebras, but can become important when considering "Lie algebras" over the integers.
Split into simpler sentences: In characteristic other than 2, these are equivalent (in the presence of bilinearity), so this distinction doesn't arise when considering real or complex Lie algebras. It can however become important, when considering "Lie algebras" over the integers.