Linked from
The 17 pages that link to S-wave, each with the reason it gives.
SeismologyBroader topic: Its inability to cross liquids proved Earth's outer core is molten.
P wavesCompared with: Unlike P waves, S waves cannot travel through liquids.
SeismogramBroader topic: Its later arrival helps distinguish seismic phases on the trace.
Earth's outer coreBroader topic: S-waves do not propagate through the liquid outer core.