Different. Sprains affect ligaments and connective tissue strains affect muscles.
Stretch or tear. A sprain is a stretch or tear of a ligament that gives stability to a joint and a strain is a stretch or tear of a muscle/tendon unit, muscle or tendon (a tendon is a fibrous cord of tissue that connects a muscle to a bone) which in most instances causes motion at a joint.
Joints can sprain. A muscle "strain" is when muscle fibers get stretched too far and/or some fibers tear. People generally call it a tear if enough fibers break, leading to some bleeding and swelling inside the muscle, resolving later with some healed scar tissue and some tightness in the area (less elastic). A joint sprains when its ligaments (whitish fibers) are stretched too far and break. Muscles don't "sprain".
See below. Muscle fibers are injured that causes muscle strain. Ligaments can be injured and the terminology is ligament sprain.
Similar, but diff. A sprain is an injury involving the stretching or tearing of a ligament or a joint capsule. Sprains occur when a joint is forced beyond its normal range of motion, such as turning or rolling your ankle. Strains are injuries that involve the stretching or tearing of muscle and/or tendon. Strains take place when a muscle is overstretched suddenly, such as pulling a hamstring.
Muscle vs ligament. Sprain is ligament injury, strain is muscle injury.
Ligament vs tendon. In general, strains are injuries to a muscle or tendon. A tendon connects the muscle to bone. A sprain is an injury to a ligament. Ligaments connect one bone to another. Both can range from mild (like a stretch with mild injury and pain) to severe (complete tear that might need surgery). See your doctor if you have severe pain, weakness, instability, swelling or an injury that doesn't heal.
Tissue difference. A strain is a stretch injury of a muscle or tendon. A sprain is a stretch injury of a ligament. A ligament connects bone to bone. A tendon connects muscle to bone.