It's just indicating how the TRS jacks are configured, in case you're making your own cables or something. If you've ever looked at a 1/4-in TRS plug, it's got three solder points on it--one to the tip, one to the ring and one to the sleeve. That schematic just shows you what wire should connect where to interface correctly with that jack. That is the standard wiring configuration for TRS connectors BTW.
They're electrical terms for the polarity and/or flow of the wiring.... hot is the positive component, cold the negative (or polarized opposite of the hot signal), and then the GND for neutral/ground connection.
Nothing will happen to you if you touch the cables - there isn't enough current in the signal to produce a shock.....