The Sum Assured is the contractual base amount of a life insurance policy. It is the minimum the insurer will pay out — death benefits and maturity benefits are calculated as Sum Assured plus accrued bonuses (in participating plans) or Sum Assured plus guaranteed additions (in non-par plans).
In LIC's endowment family, the Sum Assured is the headline number you choose at policy purchase. It drives both the premium (higher SA → higher premium) and the §80C eligibility (premiums qualify for §80C deduction only if Sum Assured is at least 10× the annual premium for policies issued post-April 2012).