What does it mean when people ask for you to 'Ping' them if they are interested in something? What is pinging?

<- this is pinging

When you put @ in front of someone's username. Basically lets them know they are wanted somewhere (in the forums) by a specific person (or if you ping groups a specific group by a specific person).

Oh I see. I have been pinging all along and I never knew it! Hahahahaha. Thanks!