This is a site
on the world wide web
whose primary content consists of links to other sites. A search engine
is a kind of portal, since it usually creates a list of links to other sites for you.
Many web portals are designed to encourage you to set your browser to start up pointing to them. These portals typically include a search engine so you can find anything you want starting from that page without having to type in a URL. They often include news, sports, weather, shopping and anything else they think might interest their audience.
Other web portals can be quite specialized, such as a web portal with all the links that might interest someone trying to decide whether they should buy a particular breed of dog.