"Not Purchasable" usually refers to one of several kinds of items in the game:
Items that are unavailable - e.g. items that are included in the data files, but simply are not available in the (unmodified) game, but are still present in the game files, so can be modded/hacked/scripted in.
These are items that are available in the game, but may not be bought. Prominent examples include:
- Many Missiles (e.g. the Remote Guided Warhead).
- Many Ships (e.g. the Aran).
- Many Weapons (e.g. the Repair Laser).
- Several Wares (e.g. the Jump Beacon).
Many ships listed as unpurchasable may be boarded