Portafilter
The handled metal holder that clamps the coffee basket into an espresso machine's group head.
The portafilter holds the filter basket of ground coffee and locks into the machine so water can be forced through under pressure. It comes in pressurised and non-pressurised versions and in different diameters.
A heavier, well-made portafilter holds temperature better, but basket type and fit matter more for taste.
Why it matters for small spaces
Portafilter diameter (often 51mm, 53mm or 58mm) determines which tamper and accessories fit your machine, so it is worth knowing yours before buying extras.