These are days that are favorable for us and good to perform/do any activities.
People choose auspicious days for marriage, house warming, business, buying a land, bike or car.
On the auspicious days, the food is always a vegetarian food. Some times people skip a meal or two.
Typical food during auspicious days include:
Sambar or Kuzhambu, Rasam, Veg side dishes.
Popular auspicious days include
You should check out tamil calendar for exact days of the auspicious days. This changes every year.