Ligaments are what hold our bones together, and they are non-contractile meaning that they are just ‘there’ – you cannot directly control their tension level. Tendons are what muscles blend into before they attach to bone (ie. muslces and tendons are part of the same ‘rope’). When you contract a muscle, the tendon that it becomes on the way to its bony attachment site is also put under tension.
Damage that occurs to a ligament (ie. tearing) due to over-tensioning is referred to as a “sprain“. Damage that occcurs to a tendon (ie. tearing) due to over-tensioning is referred to as a “strain“. When either of these terms are used in conjunction with the terms “mild“, “moderate” or “severe“, one is just further describing what percentage of the fibres of that ligament or tendon have been damaged or torn.