Answer is simple in one way and slightly confusing in another. All you have to do is look at the licence agreement.
It says:
- You may install one copy of the software on one device. That device is the “licensed device.”
- You may only use one copy of the software on the licensed device at a time.
- You may install another copy of the software on a portable device for use by the single primary user of the licensed device.
It also says, with respect to Office Home and Student specifically, For software marked “Home and Student” edition, you may install one copy of the software on up to three licensed devices in your household for use by people for whom that is their primary residence.
I'm no lawyer but it seems to me that, for the Home and Student Edition, the household effectively becomes the primary user. So you can install it on three devices which can be used by any number of people who live at the residence (as their primary residence) and on one more portable device, that again can be used by anyone who lives at the residence - except that if the portable device is in use, only two of the other devices can be used at the same time.
But I'm not a lawyer and I can see that there are other interpretations that could be put on the text.
For some reason that I can't explain, I find such things interesting.....