An adverb that affirms a statement is called an adverb of affirmation.
Examples:
- You can certainly take my car on a drive.
- I am going to attend the rally by all means.
- Of course, she is happy.
- Yes, they have arrived.
- Perhaps, you are right.
The highlighted words certainly, by all means, of course, yes and perhaps affirm what is stated in their respective sentences. Therefore, they are adverbs of affirmation.