An ISP is an Internet Service Provider. When you are connected to them, you connect to the internet through one of their gateways. When you do a
whois search to find out the personal information of a person, you will not find their personal information. What you will receive, in most cases, will be the name of the ISP, the Name Servers, the address of the ISP or the gateway, and contact information for the ISP. ISPs don't give out the personal information of their clients without good reason; they give their own out instead.