These steamed buns, with skin pinched at the top creating vertical ripples all around, are filled with broth and typically pork. They originate from Shanghai so are often known as Shanghai dumplings, or soup dumplings, or Shanghai soup dumplings, or by their Mandarin pronunciation, xia0longbao, or the abbreviation XLB.
The skin is usually thin and delicate (although there are variations with thicker dough), so it's a challenge to plop them in your mouth without breaking the skin and spilling the broth (and burning your mouth). The safest and wimpiest method is to place each dumpling in a spoon, then poke the skin and let the broth run out into the spoon.