The market data on the exchanges is currently disseminated through 8+ broadcast streams and each stream has data for a particular set of products. In order to ensure the data is streamed efficiently, the various securities/contracts have been organized into products with a unique product ID and each product will be mapped to a partition. Each partition will have a dedicated data stream.
A product is a grouping of one or many securities/contracts. A partition is a grouping of a set of products.
This is the architecture on the exchange.
In layman terms, the exchange has essentially separated the various products to ensure efficient trading and streaming of data. This also helps the exchange in cases like mass cancellations, recovery etc.
Each and every partition has a limit in terms of the number of orders it can handle. An order will be rejected if the particular partition on which the trade was queued had exceeded its limit.