Means secret sauce.
It is actually my precious chilly sauce, that usually are sent or brought from Indonesia. Whenever I took the chilly bin from refrigerator to add flavor to my food, Hiro always "whispers" to Iki "mama no himitsu so-su" (read: mama's secret sauce).
I was running out of stock so yesterday I tried to make it myself. Got simple recipe from my mom but modified based on ingredients availability here.
Sambal goreng ala Imoet
Yum yum yummy :p
(though Hiro gave me this "ewwww" face when he saw it)