What are the three main criteria for the defination of a cell

Well i didnt understand this question...so if anybody could help i would be grateful....THX :)
What are the three main criteria for the defination of a cell

Well, the question could have been referring to the Cel Theory:
1) Cells are the basic structural and functional units of life.
2) The activity and function of cells dictates the overall functioning of the organism the cells comprise.
3) Cells can only arise from the division of pre-existing cells.
(There's a fourth point, about how structure and function are inseparably linked, but that's optional I guess.)

Hope that helps! :)