The Salesforce Platform is a single, secure, and scalable platform which Salesforce applications are built on. It enables Salesforce products to be customised to individual business needs and integrated with other systems through apps from the AppExchange. Salesforce Platform is also an app development solution allowing businesses to build and deploy their own applications.
AppExchange is Salesforce's business app marketplace that lets users extend their Salesforce functionality with apps and components for every department and industry, including sales, marketing, customer service, IT, and more. AppExchange offers over 3,000 apps and components.