Port 80: HTTP
Port 80 is the default port for unencrypted web traffic.
What runs on port 80
HTTP, the original protocol of the web, listens on TCP 80. Most public websites now only use it to redirect visitors to HTTPS on 443. It is still widely used inside networks by devices that never got proper certificates.
On a home network
Nearly every router serves its admin page on port 80 on the LAN, and so do many printers, cameras, NAS boxes, smart plugs and media servers. Seeing 80 open on these devices inside your home is normal.
If port 80 is reachable from the internet
A web server answering on 80 from the internet is normal, usually just to redirect to HTTPS. A home device answering on 80 from the internet is not: it usually means router remote administration is switched on, or a camera or NAS has been forwarded, and anything typed into it, including passwords, crosses the internet unencrypted. Exposed device web panels are a main entry point for IoT botnets that try default passwords and known firmware bugs.
How to check whether it is open on your network
Check that remote management (sometimes called remote administration or WAN access) is off in your router settings and that no port forwarding rule points at 80. A port scan of your public address from outside your network will show whether it answers.
To find out whether port 80 is open on something in your home, and whether the internet can reach it, the app scans your Wi-Fi from your phone and checks your public address from the outside. It says what it checked and what it could not. Get RECON for iPhone — one-time purchase, no account, nothing leaves the device.