Under-pinning repair

Hello guys, I am working on the foundation inspection course and under-pinning was mentioned as far as a foundation wall reinforcement fix. Please let me know what under-pinning is?

" In construction or renovation, underpinning is the process of strengthening the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons: The original foundation isn’t strong or stable enough. The usage of the structure has changed."

From: https://en.wikipedia.org/wiki/Underpinning

One method of underpinning: 1:14 sec.

Various Photos: https://www.google.com/search?q=what+is+underpinning+a+foundation?&client=safari&rls=en&tbm=isch&source=iu&ictx=1&fir=vJ-IVDij-FL1OM%3A%2CrE6qyTcS8u3CeM%2C_&vet=1&usg=AI4_-kTMPPH4bX3Ue6PU7Pb1mfinZwuZHA&sa=X&ved=2ahUKEwj2pJa3oIfoAhWMW80KHRzLB9MQ_h0wA3oECAgQCg#imgrc=vJ-IVDij-FL1OM:

Thanks Larry, I can see under-pinning would be a costly endeavor!

Jim Mac