People will clean their entire house during the last few days of the year to greet and enjoy the New Year. They first distinguish necessary things from unnecessary ones, and then they try to throw away as many things as possible. After that, they wipe every nook and cranny of their houses as if they were trying not to carry over any dust to the coming year. Since the idea called 断捨離/dan-sha-ri (please see Note 1 below) has become very popular this year, I think that people try to throw away many more things than usual .
On the 31st of December, wives are usually stuck in kitchens cooking special dishes called おせち料理/osechi ryori ( please see the pictures) for the New Year Holidays, although more and more people are buying them. These dishes were developed when refrigerators didn't exist. They were basically nonperishable foods at the time. In other words, they were cooked to last for a few days so that wives did not have to cook during the New Year holidays. Because of this, the special dishes will be strong and too sweet if you cook them based on the general recipes. Speaking of nonperishable foods at the time, some kinds of sushi/寿司 were developed to last longer, as well.
I'm not sure where this idea and phrase come from, although I've heard that they came from Yoga. This means thinking about your life by means of thinking about what things around you really need and throwing away things other than those you really need. Books and magazines relating to 断捨離 are enjoying good sales.