TimR expressed precisely :
You can call it 110 or 120 interchangeably.

Yes, but one of those would be wrong.

It hasn't actually varied in my lifetime, other than the normal day to day
variation with load.

No "brownouts" then? Of course, we're not really talking about actual
voltages here, but the nomenclature instead.

That's an RMS value, the peak is around 170.

Yes, but it is best to stick to one measure throughout a discussion.

Similarly when I worked in a factory the voltage was 440, 460, or 480,
depending on who was talking, but it was all the same jolts.

As long as everyone understands each other, then there is no harm. When
using figures like that in engineering, everyone should use the
'correct' voltage in their computations.