1. He is my boss.
(What is the meaning of 'boss'? My senior in a department or the president of a company?)
2 answers
Your boss is your supervisor in whatever job you have. Employees obey the boss, who usually has his/her own boss who needs to be obeyed, etc. And yes, your boss could be the president of a company if you work directly for him/her.
Your boss can be any supervisor. She or he is anyone who is responsible for your work.
If your job is to make and serve hamburgers at McDonald's, your bosses are the shift manager, the store manager, and the president of McDonald's.
If your job is to make and serve hamburgers at McDonald's, your bosses are the shift manager, the store manager, and the president of McDonald's.