What counts as a 'prosumer' espresso machine?

Reviewers generally use the term for machines that bridge consumer convenience and commercial-grade features—things like 58mm portafilters, PID temperature control, single- or dual-boiler heating systems, and the ability to dial in grind, dose, and pressure. Built-in-grinder all-in-ones like the Breville Barista Express sit at the entry end, while standalone dual-boilers like the Rancilio Silvia Pro X represent the upper tier.