The nomination usage policy states that
Note that the usage limits above apply per website/application: the sum of traffic by all your users should not exceed the limits.
Apps must make sure that they can switch the service at our request at any time (in particular, switching should be possible without requiring a software update). If at all possible, set up a proxy and also enable caching of requests.
Not sure what sum of traffic not exceeding the limit means. Does this mean that if I have a mobile app with 100 users, I need to somehow prevent at least two or more users from placing a request within a second of each other, or does it mean that every user must respect the 1 call/second limit?