!مبارک باشه / mobarak bashe / congratulations!
I went shopping with my friend this weekend, and I bought a dress. After I paid and we were leaving the store, my friend said mobarak bashe! Then she bought something, and I told her mobarak bashe!
In many cultures, it's customary to give congratulations when you acquire something new, but that something is usually big- a car or house for example. In Iranian culture, on the other hand, whether you get a new job or buy a new car or just a new T-shirt, Iranians will use the phrase to congratulate any new possession that you acquire.