What is ping: ping is method to measure minimum time needed to send smallest possible amount of data and receive response. For ping test are used ms units (1000 miliseconds = 1 second). Usual values for optics of cable connection is 5-20ms. Wireless (2.4Ghz, 5Ghz,..) close to 30ms. Mobile connection is much worse >100ms.
Ping value affects most gaming over internet and internet telephony (skype). Less is better, reasonable value is lower than 50ms.