In Shared Server Hosting, your main dedicated server is shared with number of users who had chosen shared hosting while purchasing. Depending on server configuration, number of websites hosted on single server may vary.
Shared Server has very high configuration that can handle millions of server request and page views. But in actual, each shared hosting account is provided with some limitation in terms of Disk Space, Bandwidth or number of domains that one account can host.
Shared server is generally recommended of beginners who can initiate there small business or even blog easily.
Pricing of individual shared server account is very less as compared to Virtual Private Servers (VPS) or Dedicated Server.