This is the 6th most frequent Bulgarian word.
са
The Bulgarian word "са" means "are" (third person plural form of the verb "to be").
Here, 'са' again serves as the third person plural present tense of 'съм', used to establish the location of the subject in the sentence.
Книгите са на масата.
The books are on the table.
In this sentence, 'са' is used as the third person plural form of the verb 'съм' (to be) in the present tense, expressing a state of being.
Те са ученици.
They are students.
In this case, 'са' functions as the third person plural present tense of 'съм', describing a quality of the subject, namely the temperatures.