Patients often come into the clinic using these words interchangeably to describe anything from a twisted ankle to a pulled hamstring. They are not the same.
A sprain refers to an injured ligament. Ligaments are fibrous bands of tissue that connect your bones to each other. They provide a passive limit to the amount of movement between bones.
A strain refers to injury to a muscle or tendon. The tendons in your body are what attach your muscles to your bones.