shirttail

The shirttail (also spelled "shirt-tail") is the bottom part of a shirt (especially a dress shirt or collared shirt) that would normally be tucked below the waist of the lower garment. This becomes visible if the shirt is untucked, or if the lower garment is missing, lifted or seen from below at a low angle (for skirts particularly in the latter two examples).

External links:

• Merriam-Webster: Shirttail
• Wiktionary: Shirttail

See also:

• dress shirt
• collared shirt
• whale tail (clothing): A tangentially similar case where the underwear is visible above the waistline instead of the shirt visible below it.