Technically speaking, the "ping" is the time that a destination host (in this case the game server) takes to reply a ICMP Echo request from another host (in this case, your pc)
So it basically means how much time takes a packet to travel from your pc to the server.
Ping is like previously mentioned, the Echo request time. The larger, the longer it takes for you to click, and actually move to that point.
Lower is not always better due to sometimes pings showing as for example, sub 100 but having terrible packetloss. This will produce completely unstable and bursts of information being sent received with long waits between due to having to resend over and over again.
I think they've stop using "FULL" since C4 (i still remember the good ol'days where it was absolutely impossible to connect to Teon because it was, well, "FULL" all the time :()