The sum assured is the guaranteed lumpsum amount that an insurance policy promises to pay out when a valid claim is made — most commonly on the death of the insured person, though some policies also pay it out on maturity if the person survives the full policy term. It's the headline number that defines how much financial protection or benefit the policy actually provides.
When choosing a life insurance policy, the sum assured should be carefully sized to your family's actual financial needs — enough to replace your income for several years, pay off outstanding loans like a home loan, and fund major future goals like children's education, rather than an arbitrary round number. It's worth distinguishing sum assured from premium; a higher sum assured naturally requires a higher premium, but the relationship isn't always straightforwardly proportional.