"essentially part of salary"
Yes, bonus is part of total compensation package, but the person before said base salary. Meaning, they can never pay you below that, and it is the number on which your raise is calculated is base salary. Gross salary would include bonus and any merit awards. Over the years, bonus has been called "at risk" pay, Company Performance Incentive, and now is called Success Bonus. They changed it from "at risk" to incentive years back when it implied it was something to be lost instead of something to be gained. But if the company doesn't pay a bonus one year, you are not making anything less than you have been promised.
"Total compensation package" includes base salary, bonus/at risk salary, merit awards, and other non-cash incentives (like the points for the health program that you could spen on gift cards). "Total rewards" package includes the cash and non-cash amount, health benefits, and retirement contributions. These are all the terms used in the "Your Rewards" statement you get each year when we get covered on new salary each year.