A "tweenie" is the affectionate name for a dachshund that finishes growing between the miniature and standard weights — say 5.5 to 7 kg. They are common, especially from litters where a miniature line still carries standard-sized genes.
A tweenie is not a defect. Many owners consider it the sweet spot: robust enough to enjoy a proper walk and cope with normal life, small enough to pick up and travel with easily.
The label that should worry you
The real problem is at the other end. "Teacup", "toy", "micro" and "miniature miniature" dachshunds are sold at a premium as a rare novelty. None is a recognised variety, and there is no separate standard protecting how they are bred.
Breeding for extreme smallness tends to select for runts and to concentrate the genes behind fragile bone, dental crowding, patellar luxation, liver shunts and unstable blood sugar. A very small dachshund can be perfectly healthy, but the deliberate pursuit of tiny size is a red flag about the breeder's priorities.
