Not long ago, my neighbor had to have some foundation repairs done at his house. I live in an area of the Texas Gulf Coast where there is long term terrain subsidence. Foundations can shift and begin to crack without intervention.
If you are not familiar with repairing a foundation, the crew will dig holes around the edges of the slab. The holes go as deep as it takes to hit bedrock. Then concrete piers are poured into the holes. Once the piers dry, shims are used to level the structure, returning the foundation to a true and level condition. Once the piers go in, there is very little movement. The foundation becomes strong and firm again.