To be fair, that snippet of code is so overly convoluted that a little guidance wouldn't hurt.
Here's how I would rewrite it:
if {LOAN_IPT.INTEREST} like "*BROKER" //string match on field
then (if isnull({CARDINDX.DESCRIPTION}) then {LOAN_IPT.SHORT_NAME}&" *** SHORT NAME ***"
else {CARDINDX.DESCRIPTION})
else "" //if string match fails, return empty string
EDIT: It just occurred to me that if a string match fails, an empty string is not necessarily returned, but rather the value of the BROKER variable which could have been set elsewhere in the report. You will need to search other formulas in the report to see if any of them use that same variable (my guess is that they don't, but you never know).