Ballaaj, with a double "l" sound, as in (BU)n + (L)emon +(LA)mp + (J)ump, with the stress on the last part: -laaj, is a non-Quranic Arabic name that means "wide-faced", "light-skinned", "glowing", "beautiful". Since the meaning is good Muslims can use it. You can use it for a boy or girl. It can also be spelled as Balaaj and Balaj. There are two other non-Quranic Arabic names with the same meaning: Baalij and Balj.
Balaaj (with a light "l" and the stress on the last part: -laaj), pronounced as (BU)n + (LA)mp + (J)ump, is the Farsi name reed mat (hand-made mats made of reed and common in some parts of Asia). It can also refer to any plant from which these reed mats are made. Since the meaning is not bad, Muslims can use this word as a name. This Balaaj is not an Arabic or Quranic name.