A script parameter is information that is passed to an action or conditional script (usually from a conversation).
"For example, to do an ability check for wisdom, you could use the script gc_check_stats. So to do a specific check for say wisdom > 10, you'd enter this as a conditional for the conversation node:
gc_check_stats 4 10
(4 is the code for wisdom for this script.)
Scripts may include as many parameters as needed using both numbers and strings. 
NWScript constants are not used with script parameters.