Ping is the time it takes for your computer to send an echo request to the server, and for the server to respond, usually measured in milliseconds. If the server has many players or is farther away, the Ping will be higher. If the server has fewer players or is closer, the Ping will be lower. The higher the Ping, the longer the server takes to respond.
Ping is important, yet many players don't know what it is. If you want to know the Ping for a server, it is located at the far right on the world-select screen.
As a general rule of thumb, a world with more than 200 is not recommended for dangerous situations, 100 and below is generally lag free, and anything below 50 will have no lag.
Because Runescape runs in 600-millisecond tick intervals, the effective ping time for most actions is increased by up to 600.
To find out the highest/lowest Ping, click the arrows in the Ping column to sort the Ping into ascending/descending order.
If the Ping is "N/A", try putting the world in your favourites and it should tell you the Ping.