What does ping mean?

Ping is a rough measurement of latency/delay between one machine and another, or in other words, ping is the amount of miliseconds packages need to travel from your location to the server and back. Pings are only reliable when there are no other traffic on the link. This of course makes pings for games more reference than anything. Despite what you might think, high pings don't necessarily make lag.

And what about lag?

You can have a ping of 800ms (high latency) and be lag free. While your actions ingame will be behind, the quality of the connection can still be perfectly fine. Lag is packet loss. This is where the network has to pause and resync.... get things back in order. During lag, no packets pass through, including the ping packet. This means the time for a ping to return increases and can show a higher number than normal. Obviously no game packets pass through either."

What effect does having a high ping have?

Having a low ping is always desirable because lower latency provides smoother gameplay by allowing faster updates of game data.

If you have a high ping it means the data that's being sent from your computer to the game server is taking a long time to travel and so your movements/actions will be updated behind everyone else in game.

Which is why if your ping is high you might think you shot first and that's what is displayed on your screen, but according to the server you shot a little after the guy that killed you. Most evident on games with killcams.

Having high ping does not automatically mean that the player is laggy, and I'm sick of people thinking that having high ping is an advantage. It's the opposite, being an overall  disadvantage.

Imagine this scenario: you are awping and you have 200 ping while another player has 10 ping. During the round you shoot him 0.1 seconds before he shoots you, but he will actually get the kill because it will register for him first.

Exerpts from:

• http://forums.gametrailers.com/thread/wh...qu/1103483
  
• http://en.wikipedia.org/wiki/Ping_(video_gaming)

AWESOME JOB!!

I'd have to add, that the way srcds interpolates packets for hit registration, ping difference literally means nothing if you have the same stable rates as someone else. The delay between you doing the action and the action being registered on the server is mostly down to interp. This is why when someone else has 30.3ms lerp, but has a different ping to me, the hit registration will be excellent between us (no lerp'd shots, no lag spikes etc). It's because we're interpolating the packets at the same rate, and should hopefully be uploading and downloading packets at the same rate, so we'd technically be in sync.