When stretching forces act on an object, its shape changes. This change is called deformation. There are two kinds. In elastic deformation the object returns to its original shape and size when the forces are removed. The change is temporary. A spring that is stretched a little and then released goes straight back to its original length.
In plastic deformation the object does not return to its original shape when the forces are removed. The change is permanent. A paper clip that is bent open stays bent, and a piece of plasticine pulled out stays long.
Every spring or wire has an elastic limit. If the stretching force is small, the deformation is elastic. If the force goes past the elastic limit, the limit has been exceeded and the object is deformed plastically. After the forces are removed, a spring that has been stretched past its elastic limit stays longer than it was at the start.