Ping is a diagnostic and troubleshooting tool used to probe whether a given computer is reachable over the network. It does that by sending Echo Request ICMP packets to the target IP address and waiting for ICMP Echo Reply packets (or Pongs) from the target.
If replies are received, it is usual to tell the latency (lag) of the connection from the time that took the packet for the round trip. We can also see (or better, try to guess) how many routers the packet traveled through by looking at the TTL value (in Ping slang TTL refers to Hop Counter, nothing to do with Time to Live). When a packet is sent, the TTL is set to a given value (most times, Windows set it to 128, other times to 64 or 255. Other operating systems will set different values), when the packet is received we can read the TTL, subtract from the initial TTL (assumed 128 for Windows, or the closest power of 2 above the received TTL) and obtain the number of hops (this is deemed to fail sometimes, so it is better to use a related tool, called Traceroute) .
The Ping can also be used to calculate the MTU (Maximum Transmission Unit), which is the largest packet size in bytes that can be sent without fragmentation. However this test must be performed from a local PC, not from an online service. Related with this, but not useful for tweaking the MTU of your own system, we have set the largest packet size you can set in the box below when pinging an IPv4 address to 1470 bytes and when pinging an IPv6 address to 15000 bytes. In other words, these are the largest packets you can send from our server when pinging.