RO/DI question- "stages"

[javajoe]

I am looking into a RO/DI unit, and am seeing different satages mentions- 2stage, 3 stage, etc.
What are the stages- what gets filterd out in each stage, for instance in a 5 stage RO/DI unit?

 

[save a fish, eat chicken]

I have a KENT Maxxima 50 TFC.
The stages are:
1) 5 micron sediment filter
2) carbon filter
3) R/O membrane
4) DI resin