What it is
Ports are the numbered endpoints a server listens on, each conventionally tied to a service: 80 for HTTP, 443 for HTTPS, 22 for SSH, 21 for FTP. This check reports which of the common ones accept a connection.
Why it matters
Anything listening is something that can be attacked, so an unexpected open port is worth explaining. Database ports, admin interfaces and remote access services exposed straight to the internet are the usual findings.