Slicing of contents in a cell

Consider a cell with contents “abcdefghijklm”.
How do I ‘slice’ this to get contents ‘starting from 4th place to 8th place’?
In this case, it will be “defgh”.
(It is very similar to the python language slicing :-- aString[3:6]
I looked at LEFT and RIGHT functions. But I want to slice it starting and ending at any given position.