It's a place to put documents and information which is instantaneously accessible from virtually anywhere on the planet, at virtually no marginal cost
It's an extremely cost-effective delivery mechanism of tools for manipulating information, collaborating with other people, and controlling and monitoring real-life business processes.
In other words, why we bother with websites is because they convey knowledge and tools that make people—like your customers and staff—more efficient at what they do, or even achieve things they otherwise couldn't, without the manufacturing and distribution overheads of other media. In other words, the website is just a conduit. As with any other medium, what costs the money, and what generates the value, is developing the content.
The value of a website is a function of the value of its content. What I mean is this: How valuable is a cookbook that only produces bad-tasting food? Or a repair manual that breaks things rather than fixing them? Or an appliance that is so unwieldy that it takes more effort to use than not to? Or a road map that sends you driving off a cliff?