Star Citizen aUEC stands for Alpha United Earth Credits. The currency used in the game Star Citizen, is called United Earth Credits with "Alpha" signifying that the game is not in its final stages - it is in its Alpha stage.
With aUEC you could buy ships, weapons, gear, and upgrade ships also for other uses. Currently, Star Citizen is in Alpha, and aUEC is a temporary currency used for testing. It might reset in future updates, but it’s important for your progress now. With MMOEXP, you can easily buy aUEC to save time and enhance your gameplay.