This is the 4187th most frequent Russian word.
средняя
"Средняя" means "average" or "middle" in English.
In this sentence, "средняя" is used as an adjective meaning "average," describing a grade.
Её средняя оценка по математике — пятёрка.
Her average grade in mathematics is an A.
Here, "средняя" denotes "average," used to refer to the temperature, providing a general measure of its typical value.
Средняя температура сегодня около нуля градусов.
The average temperature today is around zero degrees.
In this example, "средняя" is used as an adjective meaning "middle," related to an institution catering to middle-school level education.