What is helioseismology?
Helioseismology is the study of wave propagation in the Sun.
Helioseismology is the study of wave propagation in the Sun. What it isn't is the study of solar seismic activity.
The Sun's interior is a turbulent place and turbulence creates waves. As the waves propagate, they interfere with each other, causing constructive interference in some circumstances (the peak of a wave plus the peak of another wave makes the peak higher in that point) and in some circumstances they destructively interfere (the peak of a wave plus the trough of another wave flattens the wave in that point). It's as these relationships shift and change that we get clues about the structure of the Sun.