The metal-handled basket-holder that locks into an espresso machine's group head. The barista grinds coffee into the basket, tamps it, locks the portafilter into the machine, and water is forced through under pressure to make espresso. Without a portafilter, an espresso machine is just a kettle.
Two words you'll hear alongside it. The basket is the perforated metal cup inside that actually holds the coffee. A naked (or bottomless) portafilter has had its spouts removed so you can watch the shot come off the underside of the basket — baristas use it to spot channelling, because the streaks are visible the moment they form.
Its other job is thermal: the portafilter is heavy brass because that mass keeps the coffee bed at a stable temperature through the shot. That's why they feel absurdly solid for what they do.
For filter coffee, the equivalent is the dripper — V60, Chemex, Kalita. Same role: it holds the bed, defines the geometry, and sets the brew's character.
