CONCATENATE AND CONCATENATEX

Any of the functions that end in X are iterators, they loop over a list of values.  This means that you would pass in a column of values to CONCATENATEX and it would loop through the lists, and combine them togather into a single string.

CONCATENATE on the other hand simply combines 2 fields togather.

Here is some additional references:

CONCATENATE: https://dax.guide/concatenate/

CONCATENATEX: https://dax.guide/concatenatex/