Most hosting accounts allow you to create subdomains. Unfortunately, the package I selected with bluehost.com does not. A subdomain is essentially a whole new website without having to purchase a new domain. You can use these to create separate areas of your domain covering a specific topic.
Say you had the name animals.com. You could create subdomains for different animals that would have names like cat.animals.com or dogs.animals.com. Each of these sites would be completely separated from your animals.com site. If you happen to use WordPress as most users do today you would need to have WordPress installed three times.