You mean the basket. The portafilter holds the basket and is inserted into the group head. They can be bottomless (naked) or have spouts.

On to baskets. You can buy single/double/triple shot sizes (typically 7/14/21 grams) but you can also buy 18/20/22/24/25g baskets. You’ll find most serious cafes use 18/20/22g baskets. Barista’s almost always love to chat so don’t be afraid to ask questions. Just be nice and they’ll tell you just about anything you want to know about pulling espresso shots.