P or Points determines how many modules you can equip on your ship.
P must be unlocked using C (Credits).
P also defines how much an allied ship costs to build.
If you have a factory equipped, you need as much R (resources) as the P cost of the ship you want to build.
The maximum P is 8000.
Additional P can be unlocked using mods.
In the base game most ships are under 6000P.