VPS plans are similar to shared plans in that both feature multiple websites hosted on a single server. However, VPS plans maintain a strict separation between clients and websites when it comes to resource allocations. Your site gets its share, and no one else may use your resources (conversely, you may not cannibalize the resources allocated to others' websites either).
Enterprise websites include very popular marketing and media sites, as well as social, travel, and other application-heavy websites. For example, Lamborghini, Coursera, and Nordstrom use AWS to host their websites. Enterprise websites need to dynamically scale resources and be highly available to support the most demanding and highly trafficked websites.
Many services offer so-called unlimited or unmetered service for whatever amount of bandwidth, disk storage and sites you use. It's important to understand that most terms of service actually do limit the definition of "unlimited" to what's considered reasonable use. The bottom line is simple: if you're building a pretty basic website, unlimited means you don't need to worry. But if you're trying to do something excessive (or illegal, immoral or fattening), the fine print in the terms of service will trigger, and you'll either be asked to spend more or go elsewhere.