Salesforce is a cloud-hosted Customer Relationship Management (CRM) product that allows companies to identify, keep track of, and strengthen relationships with existing and potential customers.
Since its creation in 1999, Salesforce has grown to be the largest Software as a Service (SaaS) CRM product in the world. Millions of users log on every day, and many of the largest companies in the world rely on it to run their sales, marketing, and other internal functions. It's an incredibly adaptable platform that combines an easy-to-use UI with powerful scripting languages to allow its customers to build a tailored product to meet their needs.
Salesforce's offerings are broken down into a number of "clouds", each offering a broad category of functionality to their users. These include:
Sales cloud / Salesforce.com - the core CRM
Service cloud - for managing customer self-service portals, call centres and other responsive support functions
Marketing cloud - for marketing automation and customer communications
Underpinning the Sales and Service clouds is a common platform that can be configured, customised, and extended by its users. Formerly known as Force.com, and now often referred to as the Lightning Platform, this Platform as a Service (PaaS) allows developers to create and install additional applications and customisations that integrate into the core Salesforce.com cloud to further customise its functionality.
You can see a quick overview of Salesforce in this promo video: