You mean in item_group.conf? That repeat_count is the number of entries of that item in the group, which affects its relative (not absolute) probability of getting obtained.
For example, a item with a repeat_count of 2 has twice the odds of being obtained than another with 1 (or nothing) as value, or half the odds when compared to another item which has this value set to 4.
For example, a item with a repeat_count of 2 has twice the odds of being obtained than another with 1 (or nothing) as value, or half the odds when compared to another item which has this value set to 4.