0 a group of students who have lessons together -- クラス
We were in the same class at school.
1 a period of time in which students are taught something -- 授業
My first class starts at 8.30.
2 a group into which products, services, or people are put according to their standard -- 等級
3 one of the groups in a society with the same social and economic position -- 階級
4 a group of similar or related things, especially plants and animals -- (生物分類上の)綱