Imagine you have a monthly membership at a video game parlour. You forget to renew the membership after a month & hence cannot play any more games. But the gaming parlour gives you extra time called a 'revival period'. During this time, if you pay the membership fee, your card becomes valid again. It's like hitting reset without losing the fun!
Your life insurance policy works the same way - After the grace period (period of time during which an insurance policy remains in force even if the premium payment is overdue), if you fail to pay your premium, your policy lapses and it enters the revival period. During this time you will stop getting the benefits from your policy. But the revival period gives you an option to revive your policy and its benefits by paying the premium amount including the interest. The revival period may vary depending upon your product type (ULIP, Term or Traditional)