To put it another way:
All living things are made up of cells.
If we go "higher", less basic, then we have things like organs - but different living things have different organs, and some living things have NO organs (for example: single-celled animals).
So:
- we can't say that all living things are made of bodies
- we can't say that all living things are made of organs
- but we CAN say that all living things are made of cells
So: a "cell" is the largest, most complex basic unit of living organisms. That is: a cell is the largest structure that ALL living things are made of. There are smaller structures that living things are made of - atoms, for example - but the cell is the largest, most complex structure that is basic (a sort of "building block") for *all* living things.