When is a wire considered high-Z?
Think at an Hi-Z wire in this way: can I connect its lead to any (reasonable) point in the circuit without having current flowing in the wire?

If yes, then the other lead of the wire is connected to a Hi-Z point of the circuit. A Hi-Z point is one connected to a very high resistance so no current can flow.

In your schematic NO wire (neither of 1,2,3,4) is Hi-Z because if you connect one of them to GND, current starts flowing and the LED lights up.
UPDATE: Wire number 3 can actually be Hi-Z, provided that the resistor attached to it has a very high ohmic value.

Hi-Z is used for example in microcontrollers when they start-up. Given that  any I/O pin can be connected to anything, and at the start time the microcontroller does not even know whether a certain own I/O pin is (will be configured as) an input or an output, those I/O are Hi-Z: you can pull them low or high, you can attach them to an input of some other IC, but nothing happens, they seem to be connected nowhere and no current can flow.

Another example where Hi-Z is desirable is in scope probes: a scope probe should be Hi-Z (as much as possible) in order to not pollute (or worse) the signal you are trying to measure.