They are those whose bad deeds are more than their good deeds.
There is an Arabic miraculous expression in presenting the following meaning: Those whose scales are light, his refuge will be an abyss.
We are in front of two types of people; people whose scales of good deeds are heavy and people whose scales of bad deeds are heavy, thus, this scale becomes heavy by good deeds and becomes light by bad deeds, not according to money.
Mentally, when we have a weigh and a weighed, we have three conditions: One pan is heavy and the other is light or the two are balanced. But the last condition is not mentioned in this Surah.