EMZETT.Intranet
In short: A private network using the same technologies as the internet (TCP/IP, HTTP), but not publicly accessible — typically an organisation’s internal network.
In more detail: Access is usually restricted to employees or devices on the internal network, often additionally reachable from outside via VPN. An intranet can host its own internal websites, wikis, or tools, without them being reachable from the public internet.
In Depth
An intranet uses the same technical foundation as the public internet — the same protocols, sometimes the same software (internal wikis, ticketing systems, dashboards often run in the browser just like any other website) — but is shielded from the public internet by firewalls and network segmentation. Devices on the intranet often have private IP addresses from reserved address ranges, which aren’t directly reachable from outside at all.
For employees who need to access internal resources while travelling or from home, a VPN is typically used: their own machine establishes an encrypted connection (“tunnel”) to the company network and appears to the intranet as if it were connected directly on-site — without the company’s firewall having to open up the rest of the user’s internet traffic.
A related term is “extranet”: a part of the intranet specifically opened up for external partners (e.g. suppliers), without opening up the entire internal network.