These plants are called Air Plants. Their true name are Tillandsia. The reason why they are nicknamed "Air Plants" is because they get the majority of their nutrients from the air around them.
Caring for Your Air Plants
Tillandsias grow differently than most other house plants, so they can be confusing to the beginner. They are really very hardy, and require much less attention than other house plants. The following simplifies the instruction but you can scroll down for much more specific information.
Provided the atmosphere is not too dry they can survive with water misting and the occasional bath.
Never plant in soil.
Give them bright, filtered light.
Protect them from frosts.
If you are growing them indoors and the air is dry, you will need (at minimum) to submerge the plant in water for 2-3 hours about every two weeks.
In a shaded-house or unheated home, you can use a soaking mist once or twice a week in summer, once a month in cooler weather.