Note: This is only an attempt at such, so please let me know where it falls insufficient.

First, some definitions:

federation n: an organization formed by merging several groups or parties

federation n: a union of political organizations [syn: confederation, confederacy, federation]

federation n: the act of constituting a political unity out of a number of separate states or colonies or provinces so that each member retains the management of its internal affairs

Now, I would propose we explain what federation is using some combination of the three definitions above.

Each instance can be thought of as its own country, state, province, etc., only there is no central authority, unlike the E.U., Germany, Canada, U.S.A., Mexico, etc. — aside from maybe those that dictate the ActivityPub protocol, as they lay down the rules for how instances interact, but still do not technically dictate whether that cooperation or interaction must take place — each instance retaining management and autonomy of its internal affairs. As a consequence, each instance can have its own governing body and laws or rules residents and visitors are required to abide by.

To make permanent residence, one needs a valid address within the jurisdiction or control of the state or government they wish to be under. If that state or government is federated with another, a citizen of one may be given the opportunity to freely trade, communicate with, or move around between the two countries, in accordance to whatever agreements may be in place. To permanently move to another, one must both be accepted and granted new residence or address within the country in which one wants to join. In the case of Email, ActivityPub, and others, agreements generally surround communication and the trading of messages, and addresses granted by those servers, or instances, providing access to the larger network.