Ping is a network command that checks whether a machine can be reached on an IP network and measures how long a message takes to make the round trip.
It sends a small packet (an echo request from the ICMP protocol) to an IP address or a domain name, and waits for the reply. The result shows whether the machine responds, the round-trip time in milliseconds (latency) and the packet loss rate.
It is often the first reflex when diagnosing a connection problem: is the server online, is the network slow, are packets being lost along the way? No response does not prove the machine is down, since many firewalls deliberately block these requests.
By extension, to ping someone means to give them a quick nudge by message.
Why it matters when hiring
Little hiring impact: every network, systems or DevOps profile knows ping. It is, however, a good starting point for a troubleshooting question in an interview, to see how the candidate reasons when a machine stops responding.