Step 1: Concept
Hooke's Law states that within the elastic limit, stress is directly proportional to strain.
Step 2: Meaning
Stress is the force per unit area, and strain is the deformation per unit length.
Step 3: Analysis
The constant of proportionality that relates these two is the Modulus of Elasticity (also known as Young's Modulus). It measures the "stiffness" of a material.
Step 4: Conclusion
This ratio is defined as the Modulus of Elasticity.
Final Answer: (B)