What is the meaning of portal?

noun

• A grand and imposing entrance (often extended metaphorically. )
  • usage: "the portals of the cathedral"; "the portals of heaven"; "the portals of success"
• A site that the owner positions as an entrance to other sites on the internet.
  • usage: "a portal typically has search engines and free email and chat rooms etc."
  • synonyms: portal site
• A short vein that carries blood into the liver.
  • synonyms: portal vein, hepatic portal vein, vena portae