Your IDE may not index (find) the constants stored in the database, nor those in the .lang language file arrays (introduced from Zen Cart 158), so code inspections may flag these constants as "undefined".

This script generates two local php files containing generated defines from

a) the configuration_keys/constants in the database
b) the language constants from the arrays in .lang language files

Hopefully your IDE will index these and clear the false "undefined" errors.