A “9-inch grinder” is a type of handheld angle grinder, using a ~ 9-inch (≈ 230 mm) disc. Angle grinders are high-speed rotary tools designed for cutting, grinding, polishing, or abrasive work on materials like metal, concrete, masonry, stone, or tile.
A Bosch 9′′ grinder — often part of Bosch’s “Professional” power-tool lineup — is built for heavy-duty jobs, more demanding than smaller 4.5–5′′ grinders. It sacrifices some of the compactness and lightness of smaller grinders for more disc diameter, more cutting/grinding capacity, and generally higher power.