A "dear boss letter" is a letter that someone writes to their boss to express their feelings about their job. It can be good feelings or bad feelings. It is called a "dear boss" letter because the person writing the letter is talking directly to their boss, like they are sitting down and having a conversation.
Sometimes people write dear boss letters when they are unhappy with their job. They might write about things they don't like, such as feeling overworked or not being appreciated. They may also write about how they think their job could be better.
Other times, people write dear boss letters to say good things. They might write about how much they enjoy their job, how great their boss is, or how much they appreciate their coworkers.
Overall, a dear boss letter is a way for someone to express their thoughts and feelings about their job to their boss. It can be a good way to communicate, even if it's hard to say things out loud.