What is strain?

What is strain?

The relative change in length or shape which is made by applying a force from outside is called strain. 

Strain is simply the measure of how much an object is stretched or deformed. Strain occurs when force is applied to an object. Strain deals mostly with the change in length of the object.

An example of strain is a pulled muscle. An example of strain is reading a book in the dark, causing pressure on the eyes.