Ping is the round-trip time, in milliseconds, for a tiny packet to travel from your device to a server and back. Lower is better, it directly controls how "snappy" the internet feels.
Jitter is the standard deviation of ping. A connection that bounces between 20 ms and 120 ms feels worse than a stable 90 ms line, because real-time apps can't compensate for the variance. Aim for jitter under 10 ms for gaming and under 30 ms for video calls.
When packets vanish entirely, applications must retransmit, which feels like a hiccup or stutter. 0-0.5% is normal. Anything over 1% is a problem , usually a faulty cable, overheating modem, or congested WiFi channel.