Answer:
An intranet is a private network with limited access. It could be an internal network within a company, or possibly accessible by authorized customers, but not to the general public.
The internet is an open international network that is available to everyone. An intranet may often have access to the internet via a gateway, but external access to the intranet is limited or unavailable.
An internet is a public network whereas an intranet is a private network only available to trusted clients or employees. Intranets are commonly available outside the company via a VPN (which makes them an extranet).