Plasticity is the property of a soil which allows it to be deformed rapidly, without rupture.

Explanation:
When a soil is subjected to an external force or load, it deforms. The deformation may be elastic or plastic. Elastic deformation is temporary and the soil returns to its original shape after the load is removed. Plastic deformation, on the other hand, is permanent and the soil does not return to its original shape after the load is removed. The property of a soil which allows it to be deformed rapidly, without rupture, is called plasticity.

Some important points regarding plasticity of soil are:

- Plasticity is a measure of the amount of deformation a soil can undergo without rupture or failure.
- Soils with high plasticity can be molded into different shapes and retain their shape, while soils with low plasticity tend to crumble or break apart.
- The plasticity of a soil depends on its mineralogical composition, as well as its moisture content and compaction.
- The plastic limit (PL) and liquid limit (LL) are two important parameters used to quantify the plasticity of a soil. The difference between the liquid limit and plastic limit is known as the plasticity index (PI).
- Soils with high plasticity have a high PI, while soils with low plasticity have a low PI.

In civil engineering, the plasticity of soils is an important property to consider when designing foundations, embankments, and other earthworks. Soils with high plasticity are more difficult to work with and may require special construction techniques or stabilization measures to prevent failure.