What is the difference between strain and deflection?

Strain is the load an object is seeing, and it's calculated in a similar way to how pressure is calculated. If you're using a wire with a cross-section area of one to lift an object with the weight of one, then the strain will also be one. Deflection is how much the object is changing shape by that load. For a car suspension deflection would be how much the springs gets compressed by the weight of the vehicle.