Crop top

A crop top (or a belly shirt, tummy top, or half shirt) is a kind of shirt. Crop tops do not cover all of the middle section of the wearer's body. A person wearing a crop top will have part of their belly and back showing. There are many kinds of crop tops, and most styles show the wearer's belly button. Other styles can show the wearer's waist, or the bottom of their ribs.
Crop tops are popular in the Western world. They are common in areas with a warm climate.
Crop tops were popular in the 1990s when movie actresses and female pop music singers wore them. They are popular again in the 2010s.
Crop tops are seen as trendy and attractive.
A crop top does not keep the wearer's middle section warm because they do not cover all of it. So, crop tops are more comfortable for hot weather and exercising.
Other types.
There is a way to make a temporary crop top with a normal shirt. The wearer can lift their shirt to show as much of their belly as they want, and then make it stay like that by tying the lifted end of the shirt into a knot. This is a common and flexible alternative to a regular crop top.
Low-rise pants or mini skirts are sometimes worn with a crop top. This shows more skin beneath the wearer's belly button.