1) Quantum mechanic 
Second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the more usual mechanism of diffusion. Heat takes the place of pressure in normal sound waves. This leads to a very high thermal conductivity. It is known as `second sound` because the wave motion of heat is similar to the propagatio.....
Synonym for second heart sound ... The second sound heard on auscultation of the heart; signifies the beginning of diastole and is due to closure of the semilunar valves. ... Synonym: second sound. ... (05 Mar 2000) ... 
Type: Term Synonyms: second heart sound