Corporate sales are, in simple terms, sales made between two large companies. For example, let's say a company called Computers R Us who sells computers speak to UPS and deliver a pitch to them explaining about their products. UPS agree to shake hands on a sales deal that Computers R Us kit out all of their USA offices with computers. This would mean that Computers R Us would be providing UPS with thousands of computers worth a significant amount of money, and this would definitely be seen as a corporate sale. Not only because the deal is between two massive companies, but because the deal means lots of money will be exchanging hands and the profit for the vendor (Computers R Us in this hypothetical case) would be huge. This sale is seen as a corporate sale.
Those that work in a corporate sales team would also find their job was very different to someone that worked in a consumer sales team. Someone in a consumer sales team usually has to sell a product by telephone or face to face in a store, and from then on, it's pretty straight forward: The customer either goes with the offer or declines the sale. In corporate sales though, it's slightly different.
People working in corporate sales usually work very hard at maintaining their relationships with their clients which isn't done on such a large scale with consumer sales. For example, going back to our hypothetical situation, Computers R Us would very likely invite UPS to events and dinners to ’keep in with them’. Freebies may also be thrown in. This can be simply secure the client.