. Restricted Stock Units (RSUS)-Case 1 Under its restricted stock unit (RSU) plan, Delta Airline grants RSUS representing 6 million of its $2 par common shares to certain key executives at January 1, 2021. The shares are subject to forfeiture if employment is terminated within three years. Shares have a current market price of $15 per share. Subsequently, the share price fluctuated and prices of $18, $20, $17 were noticed during the vesting period. Question: What does vesting mean? What is the vesting period for this RSU? What is the difference between the course of expiration of stock option exercise and forfeiture of stock option? What is the difference between Cliff vesting and Graded Vesting? What is the total compensation Expense during the vesting period and make necessary entries, if any, on January 1, 2021, December 31, 2021, 2022, 2023 and 2024, assuming no forfeiture