Expansion points, often abbreviated XP, are a currency commonly used in Imperium Offtopicum to expand a player's territorial holdings. In most early IOTs, players start with set number of provinces, and can expand into as many as their XP allow each turn.
The exact number of XP that a player receives, or can spend, varies with the games. TF (and most of the original IOTs), for example, usually has players start with five provinces and be able to spend five XP per turn, or five provinces. Likewise, sometimes provinces cost more than one XP, such as the earlier-used "distance penalty," whereby provinces far away from one's home territory would cost more to settle.
In some games, XP can be traded for other bonuses, allowing quite a bit of intrigue, especially when coupled with units of currency such as gold. Other times, they can be traded for more attacks.
In many games, players do not receive any XP if they are at war.
It should be noted that ever since For All the Marbles and Fiat Lux, the use of XP has been deprecated in favour of a more mobile expansion with the game currency or with armies.