If you've played an online game before, you might've heard of the terms high ping or high packet loss when used to describe a bad connection.
Ping is used to measure latency and latency is basically the time it takes for a signal to go from your device to the server and then return.
High ping is thus high latency and basically means there's a greater delay between what you do gets sent to the game server and what others do showing up on your screen. Ping is measured in milliseconds and a ping in the 3 digits can be considered above average.
Pack loss on the other hand is when packets of data fail to reach their destination. 5% package loss can already be considered bad.
Some games allow you to visualize your package loss in the form of a graph. Horrendous package loss can even appear as a barcode.