1. Elastic Deformation: This is a temporary change in shape that is reversible. Imagine stretching a rubber band. It changes shape, but when you release it, it springs back to its original form. Rocks can behave similarly under stress, but there's a limit to how much stress they can handle before they transition to the next type of deformation.

2. Plastic Deformation: This is a permanent change in shape. Think of bending a metal paperclip. Once bent, it doesn't easily return to its original shape. Rocks under sufficient stress can also deform permanently, leading to folds and other geological features.