Plain version: follow the life of a policy. You ask (application), the insurer delivers the contract (policy), and later the contract gets edited (endorsement). At the end it may be ended early (cancellation), run out for nonpayment (lapse), or be saved by a late payment within the allowed time (grace period).
Application: the applicant's request for coverage and the source of underwriting information.
Policy: the written contract the insurer issues.
Endorsement: a form attached to the policy that changes its terms, for example adding coverage for newly bought jewelry mid-term. A change made after issue is an endorsement, not a new application.
Cancellation: ending a policy before its term is over, for example by the insurer's written notice mid-term.
Lapse: coverage ends because the premium was not paid.
Grace period: extra time after the premium due date during which payment keeps coverage in force.