In simple terms, a Voltage is the difference in the electric potential between two points or in other words, a difference in how much electrons are attracted to one point by comparison to how much electrons are attracted to another.

So technically you can’t actually have a Voltage with just one point.

So why do you hear Voltage mentioned as being a characteristic that can be measured at one point of a circuit?

Well, in practice what it’s done in practice in Electronics is for example to treat one side of the power source as being the reference to measure voltage (say, the negative side of the battery) - which we the call Ground - and then we can say there is a “voltage” at any point in the circuit as a shortcut for the difference in electric potential between that point of the circuit and the one we conventioned as being the reference one.

(Notice how when using a Voltimeter or a Multimeter in Voltage mode to measure the voltage you need to used TWO probes and are told to put the black probe on a Ground line)

So because this reference point when measuring the different in electric potentials between two points is a convention, it’s perfectly possible to use a different convention so that some or even all “voltage” values we negative.