Critical. A vulnerability whose exploitation could allow code execution without user interaction. These scenarios include self-propagating malware (e.g. network worms), or unavoidable common use scenarios where code execution occurs without warnings or prompts. This could mean browsing to a web page or opening email.
A strain is a stretching or tearing of muscle or tendon. A tendon is a fibrous cord of tissue that connects muscles to bones. Strains often occur in the lower back and in the hamstring muscle in the back of your thigh. Initial treatment for both sprains and strains includes rest, ice, compression and elevation.
Stress is the force per unit area on a body that tends to cause it to change shape. Stress is a measure of the internal forces in a body between its particles. These internal forces are a reaction to the external forces applied on the body that cause it to separate, compress or slide.