ISP stands for Internet Service Provider. It is a company that provides internet connectivity to its customers. However, ISP in Outlook specifically refers to the "Internet Email Settings" that are required to set up an internet email account in Outlook. These settings include the incoming and outgoing server address, username, password, and other specific requirements that vary depending on the email service provider. By configuring the ISP settings correctly in Outlook, users can send and receive emails through their internet email service.