Statisticians use technical terms to refer to specific values in their calculations: "mean," "median," and "mode." Each one of these is a type of average. The word "average" is a broad concept that serves our simple needs that do not require complicated calculations. To learn more about these concepts, take a look here:
https://en.wikipedia.org/wiki/AverageFor the word "average," should we use معدل or متوسط?
Both are used in academic and colloquial discourse. In this article, the word معدل is used:
https://mawdoo3.com/كيف_يتم_حساب_المعدلOn this page, however, the word متوسط is used:
https://ar.wikipedia.org/wiki/متوسط_(إحصاء)Do I have a preference? There are two things that I do not like about the word متوسط:
1. It can be confused with the adjective متوسط ("medium").
2. It gives the impression that the average is somehow in the middle of the spread of values being averaged.
It is interesting to note that the word average is derived from the Arabic word عوار. To learn more, look here:
https://www.etymonline.com/word/average