Fixed-width vs. delimited text
When you’re splitting text to columns, Excel needs to know where to make the splits.
With fixed-width splitting, Excel splits the text at specific character counts. So it might split the text at the 5th, 15th, and 27th characters.
Delimited splitting, on the other hand, takes place when Excel sees certain characters. It might split the text at every comma, tab, or space that it finds.