Linked from
The 8 pages that link to Earth's outer core, each with the reason it gives.
P wavesBroader topic: P waves cross this liquid layer, but change speed and direction within it.
S-waveBroader topic: Its liquid state cannot support the shear motion of S-waves.
Core–mantle boundaryBroader topic: It forms the metallic, liquid side of the interface.
GeodynamoBroader topic: Its electrically conducting fluid is the moving medium of Earth’s geodynamo.