Internet Service Providers, or ISPs, are companies that provide access to the Internet such as Comcast or AT&T. A visitor to your site might appear as an ISP because they are connected through a public network which is not affiliated with an organization. While RTP is pretty good at identifying ISPs, occasionally one will make it onto your Organizations page.
If RTP makes a mistake and doesn't identify an ISP, it will end up on you Organizations page. If you notice an ISP in your Organizations page, you can mark it as such by selecting the organization in question, clicking the Choose Action drop-down menu, and selecting Set as ISP
Doing this will mark that organization as an ISP, and will help RTP learn to better identify ISPs in the future.